diff --git a/.eslintrc.js b/.eslintrc.js
index 5fbced0c04f6..cce09f2050a7 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -9,7 +9,7 @@
 module.exports = {
   extends: [
     './packages/eslint-config-fb-strict/index.js',
-    'plugin:import/errors',
+    'plugin:import/errors'
   ],
   parser: 'babel-eslint',
   rules: {
@@ -20,15 +20,16 @@ module.exports = {
     'max-len': 0,
     'no-multiple-empty-lines': 1,
     'import/no-duplicates': 2,
-    'import/no-unresolved': [2, { ignore: ['^types/'] }],
+    'import/no-unresolved': [2, {ignore: ['^types/']}],
     // This has to be disabled until all type and module imports are combined
     // https://github.com/benmosher/eslint-plugin-import/issues/645
     'import/order': 0,
     // These has to be disabled until the whole code base is converted to ESM
     'import/default': 0,
     'import/named': 0,
+    'unicorn/filename-case': [2, {case: 'snakeCase'}]
   },
-  plugins: ['markdown', 'import'],
+  plugins: ['markdown', 'import', 'unicorn'],
   overrides: [
     // to make it more suitable for running on code examples in docs/ folder
     {
@@ -43,22 +44,31 @@ module.exports = {
         'no-unused-vars': 0,
         'consistent-return': 0,
         'import/no-unresolved': 0,
-        'sort-keys': 0
-      },
+        'sort-keys': 0,
+        'unicorn/filename-case': 0
+      }
     },
     {
       files: ['examples/**/*'],
       rules: {
         'babel/func-params-comma-dangle': 0,
         'import/order': 0,
-        'import/no-unresolved': [2, { 'ignore': ['^react-native$'] }]
-      },
+        'import/no-unresolved': [2, {ignore: ['^react-native$']}],
+        'unicorn/filename-case': 0
+      }
     },
     {
       files: ['scripts/**/*', 'integration_tests/**/*'],
       rules: {
         'babel/func-params-comma-dangle': 0,
-      },
+        'unicorn/filename-case': 0
+      }
     },
-  ],
+    {
+      files: ['**/__mocks__/**/*', 'website/**/*', '**/jest-runtime/**/*', '**/src/Console*'],
+      rules: {
+        'unicorn/filename-case': 0
+      }
+    }
+  ]
 };
diff --git a/examples/react-native/.flowconfig b/examples/react-native/.flowconfig
index 2aa9a60e3b2a..31558d3ba74f 100644
--- a/examples/react-native/.flowconfig
+++ b/examples/react-native/.flowconfig
@@ -26,7 +26,7 @@ experimental.strict_type_args=true
 
 munge_underscores=true
 
-module.name_mapper='^image![a-zA-Z0-9$_-]+$' -> 'GlobalImageStub'
+module.name_mapper='^image![a-zA-Z0-9$_-]+$' -> 'global_image_stub'
 module.name_mapper='^[./a-zA-Z0-9$_-]+\.\(bmp\|gif\|jpg\|jpeg\|png\|psd\|svg\|webp\|m4v\|mov\|mp4\|mpeg\|mpg\|webm\|aac\|aiff\|caf\|m4a\|mp3\|wav\|html\|pdf\)$' -> 'RelativeImageStub'
 
 suppress_type=$FlowIssue
diff --git a/fixtures/parserTests.js b/fixtures/parser_tests.js
similarity index 100%
rename from fixtures/parserTests.js
rename to fixtures/parser_tests.js
diff --git a/package.json b/package.json
index 8355aaa24505..afe746cfd079 100644
--- a/package.json
+++ b/package.json
@@ -28,6 +28,7 @@
     "eslint-plugin-import": "^2.6.0",
     "eslint-plugin-markdown": "^1.0.0-beta.6",
     "eslint-plugin-react": "^7.1.0",
+    "eslint-plugin-unicorn": "^2.1.2",
     "flow-bin": "^0.48.0",
     "glob": "^7.1.1",
     "graceful-fs": "^4.1.11",
@@ -114,7 +115,7 @@
     "transform": {
       "^.+\\.js$": "<rootDir>/packages/babel-jest"
     },
-    "setupTestFrameworkScriptFile": "<rootDir>/testSetupFile.js",
+    "setupTestFrameworkScriptFile": "<rootDir>/test_setup_file.js",
     "snapshotSerializers": [
       "<rootDir>/packages/pretty-format/build/plugins/convert_ansi.js"
     ],
@@ -130,5 +131,6 @@
     "testMatch": [
       "**/*.test.js"
     ]
-  }
+  },
+  "dependencies": {}
 }
diff --git a/packages/jest-cli/src/__tests__/generate_empty_coverage.test.js b/packages/jest-cli/src/__tests__/generate_empty_coverage.test.js
index c34801e7b2a9..8f2749c6c20a 100644
--- a/packages/jest-cli/src/__tests__/generate_empty_coverage.test.js
+++ b/packages/jest-cli/src/__tests__/generate_empty_coverage.test.js
@@ -11,7 +11,7 @@
 
 const os = require('os');
 
-const generateEmptyCoverage = require('../generateEmptyCoverage');
+const generateEmptyCoverage = require('../generate_empty_coverage');
 
 jest.mock('jest-runtime', () => {
   const realRuntime = require.requireActual('jest-runtime');
diff --git a/packages/jest-cli/src/__tests__/search_source.test.js b/packages/jest-cli/src/__tests__/search_source.test.js
index 765c1caf1cc5..6d30fb8e233d 100644
--- a/packages/jest-cli/src/__tests__/search_source.test.js
+++ b/packages/jest-cli/src/__tests__/search_source.test.js
@@ -34,7 +34,7 @@ describe('SearchSource', () => {
 
   beforeEach(() => {
     Runtime = require('jest-runtime');
-    SearchSource = require('../SearchSource');
+    SearchSource = require('../search_source');
     normalize = require('jest-config').normalize;
   });
 
@@ -415,7 +415,7 @@ describe('SearchSource', () => {
     });
 
     it('returns empty search result if no related tests were found', () => {
-      const input = ['no tests.js'];
+      const input = ['no_tests.js'];
       const data = searchSource.findRelatedTestsFromPattern(input);
       expect(data.tests).toEqual([]);
     });
diff --git a/packages/jest-cli/src/__tests__/test_root/no tests.js b/packages/jest-cli/src/__tests__/test_root/no_tests.js
similarity index 100%
rename from packages/jest-cli/src/__tests__/test_root/no tests.js
rename to packages/jest-cli/src/__tests__/test_root/no_tests.js
diff --git a/packages/jest-cli/src/__tests__/test_runner.test.js b/packages/jest-cli/src/__tests__/test_runner.test.js
index 1a86a2cceb33..7cba6bf20eee 100644
--- a/packages/jest-cli/src/__tests__/test_runner.test.js
+++ b/packages/jest-cli/src/__tests__/test_runner.test.js
@@ -10,9 +10,9 @@
 
 'use strict';
 
-const TestRunner = require('../TestRunner');
-const TestWatcher = require('../TestWatcher');
-const SummaryReporter = require('../reporters/SummaryReporter');
+const TestRunner = require('../test_runner');
+const TestWatcher = require('../test_watcher');
+const SummaryReporter = require('../reporters/summary_reporter');
 
 let workerFarmMock;
 
@@ -27,8 +27,8 @@ jest.mock('worker-farm', () => {
   return mock;
 });
 
-jest.mock('../TestWorker', () => {});
-jest.mock('../reporters/DefaultReporter');
+jest.mock('../test_worker', () => {});
+jest.mock('../reporters/default_reporter');
 
 test('.addReporter() .removeReporter()', () => {
   const runner = new TestRunner({}, {});
diff --git a/packages/jest-cli/src/__tests__/test_sequencer.test.js b/packages/jest-cli/src/__tests__/test_sequencer.test.js
index 45d74c2ce0e2..82982eb25d2d 100644
--- a/packages/jest-cli/src/__tests__/test_sequencer.test.js
+++ b/packages/jest-cli/src/__tests__/test_sequencer.test.js
@@ -12,7 +12,7 @@ jest.mock('fs');
 const fs = require('fs');
 const path = require('path');
 
-const TestSequencer = require('../TestSequencer');
+const TestSequencer = require('../test_sequencer');
 
 const FAIL = 0;
 const SUCCESS = 1;
diff --git a/packages/jest-cli/src/__tests__/watch.test.js b/packages/jest-cli/src/__tests__/watch.test.js
index 145ffb654e3e..a544e6fb24b2 100644
--- a/packages/jest-cli/src/__tests__/watch.test.js
+++ b/packages/jest-cli/src/__tests__/watch.test.js
@@ -11,14 +11,14 @@
 'use strict';
 
 const chalk = require('chalk');
-const TestWatcher = require('../TestWatcher');
+const TestWatcher = require('../test_watcher');
 const {KEYS} = require('../constants');
 
 const runJestMock = jest.fn();
 
 jest.doMock('chalk', () => new chalk.constructor({enabled: false}));
 jest.doMock(
-  '../runJest',
+  '../run_jest',
   () =>
     function() {
       const args = Array.from(arguments);
diff --git a/packages/jest-cli/src/__tests__/watch_filename_pattern_mode.test.js b/packages/jest-cli/src/__tests__/watch_filename_pattern_mode.test.js
index b88083bada53..acd67316c488 100644
--- a/packages/jest-cli/src/__tests__/watch_filename_pattern_mode.test.js
+++ b/packages/jest-cli/src/__tests__/watch_filename_pattern_mode.test.js
@@ -28,7 +28,7 @@ jest.mock('ansi-escapes', () => ({
 }));
 
 jest.mock(
-  '../SearchSource',
+  '../search_source',
   () =>
     class {
       constructor(context) {
@@ -68,7 +68,7 @@ jest.doMock('chalk', () =>
 );
 
 jest.doMock(
-  '../runJest',
+  '../run_jest',
   () =>
     function() {
       const args = Array.from(arguments);
@@ -81,7 +81,7 @@ jest.doMock(
     },
 );
 
-jest.doMock('../lib/terminalUtils', () => ({
+jest.doMock('../lib/terminal_utils', () => ({
   getTerminalWidth: () => terminalWidth,
 }));
 
diff --git a/packages/jest-cli/src/__tests__/watch_test_name_pattern_mode.test.js b/packages/jest-cli/src/__tests__/watch_test_name_pattern_mode.test.js
index e93e28548bcc..778aff30882c 100644
--- a/packages/jest-cli/src/__tests__/watch_test_name_pattern_mode.test.js
+++ b/packages/jest-cli/src/__tests__/watch_test_name_pattern_mode.test.js
@@ -28,7 +28,7 @@ jest.mock('ansi-escapes', () => ({
 }));
 
 jest.mock(
-  '../SearchSource',
+  '../search_source',
   () =>
     class {
       findMatchingTests(pattern) {
@@ -44,7 +44,7 @@ jest.doMock('chalk', () =>
 );
 
 jest.doMock(
-  '../runJest',
+  '../run_jest',
   () =>
     function() {
       const args = Array.from(arguments);
@@ -95,7 +95,7 @@ jest.doMock(
     },
 );
 
-jest.doMock('../lib/terminalUtils', () => ({
+jest.doMock('../lib/terminal_utils', () => ({
   getTerminalWidth: () => terminalWidth,
 }));
 
diff --git a/packages/jest-cli/src/cli/getJest.js b/packages/jest-cli/src/cli/get_jest.js
similarity index 100%
rename from packages/jest-cli/src/cli/getJest.js
rename to packages/jest-cli/src/cli/get_jest.js
diff --git a/packages/jest-cli/src/cli/index.js b/packages/jest-cli/src/cli/index.js
index 5b4a8d0a6045..71b0d6571d33 100644
--- a/packages/jest-cli/src/cli/index.js
+++ b/packages/jest-cli/src/cli/index.js
@@ -22,15 +22,15 @@ import {readConfig} from 'jest-config';
 import {version as VERSION} from '../../package.json';
 import args from './args';
 import chalk from 'chalk';
-import createContext from '../lib/createContext';
-import getJest from './getJest';
-import getMaxWorkers from '../lib/getMaxWorkers';
-import handleDeprecationWarnings from '../lib/handleDeprecationWarnings';
-import logDebugMessages from '../lib/logDebugMessages';
-import preRunMessage from '../preRunMessage';
-import runJest from '../runJest';
+import createContext from '../lib/create_context';
+import getJest from './get_jest';
+import getMaxWorkers from '../lib/get_max_workers';
+import handleDeprecationWarnings from '../lib/handle_deprecation_warnings';
+import logDebugMessages from '../lib/log_debug_messages';
+import preRunMessage from '../pre_run_message';
+import runJest from '../run_jest';
 import Runtime from 'jest-runtime';
-import TestWatcher from '../TestWatcher';
+import TestWatcher from '../test_watcher';
 import watch from '../watch';
 import yargs from 'yargs';
 
diff --git a/packages/jest-cli/src/generateEmptyCoverage.js b/packages/jest-cli/src/generate_empty_coverage.js
similarity index 100%
rename from packages/jest-cli/src/generateEmptyCoverage.js
rename to packages/jest-cli/src/generate_empty_coverage.js
diff --git a/packages/jest-cli/src/jest.js b/packages/jest-cli/src/jest.js
index bced97273c0a..4e1e0cc46074 100644
--- a/packages/jest-cli/src/jest.js
+++ b/packages/jest-cli/src/jest.js
@@ -10,9 +10,9 @@
 
 import {version as VERSION} from '../package.json';
 
-import SearchSource from './SearchSource';
-import TestRunner from './TestRunner';
-import TestWatcher from './TestWatcher';
+import SearchSource from './search_source';
+import TestRunner from './test_runner';
+import TestWatcher from './test_watcher';
 import {run, runCLI} from './cli';
 
 module.exports = {
diff --git a/packages/jest-cli/src/lib/__tests__/format_test_name_by_pattern.test.js b/packages/jest-cli/src/lib/__tests__/format_test_name_by_pattern.test.js
index f15810edbb5f..69b12e137ae6 100644
--- a/packages/jest-cli/src/lib/__tests__/format_test_name_by_pattern.test.js
+++ b/packages/jest-cli/src/lib/__tests__/format_test_name_by_pattern.test.js
@@ -10,7 +10,7 @@
 
 'use strict';
 
-const formatTestNameByPattern = require('../formatTestNameByPattern');
+const formatTestNameByPattern = require('../format_test_name_by_pattern');
 
 describe('for multiline test name returns', () => {
   const testNames = [
diff --git a/packages/jest-cli/src/lib/__tests__/get_max_workers.test.js b/packages/jest-cli/src/lib/__tests__/get_max_workers.test.js
index dc9e2eddadb1..1056566a22af 100644
--- a/packages/jest-cli/src/lib/__tests__/get_max_workers.test.js
+++ b/packages/jest-cli/src/lib/__tests__/get_max_workers.test.js
@@ -8,7 +8,7 @@
 * @emails oncall+jsinfra
 */
 
-const getMaxWorkers = require('../getMaxWorkers');
+const getMaxWorkers = require('../get_max_workers');
 
 jest.mock('os', () => ({
   cpus: () => ({length: 4}),
diff --git a/packages/jest-cli/src/lib/__tests__/is_valid_path.test.js b/packages/jest-cli/src/lib/__tests__/is_valid_path.test.js
index cf1837b1aa7f..e84168d28d4c 100644
--- a/packages/jest-cli/src/lib/__tests__/is_valid_path.test.js
+++ b/packages/jest-cli/src/lib/__tests__/is_valid_path.test.js
@@ -9,7 +9,7 @@
 */
 
 const path = require('path');
-const isValidPath = require('../isValidPath');
+const isValidPath = require('../is_valid_path');
 
 const rootDir = path.resolve(path.sep, 'root');
 
diff --git a/packages/jest-cli/src/lib/__tests__/log_debug_messages.test.js b/packages/jest-cli/src/lib/__tests__/log_debug_messages.test.js
index e4a369302fcf..d68ccbfcc2cc 100644
--- a/packages/jest-cli/src/lib/__tests__/log_debug_messages.test.js
+++ b/packages/jest-cli/src/lib/__tests__/log_debug_messages.test.js
@@ -10,7 +10,7 @@
 
 'use strict';
 
-const logDebugMessages = require('../logDebugMessages');
+const logDebugMessages = require('../log_debug_messages');
 
 jest.mock('../../../package.json', () => ({version: 123}));
 
diff --git a/packages/jest-cli/src/lib/__tests__/prompt.test.js b/packages/jest-cli/src/lib/__tests__/prompt.test.js
index 9598621b8270..a8965aa1429b 100644
--- a/packages/jest-cli/src/lib/__tests__/prompt.test.js
+++ b/packages/jest-cli/src/lib/__tests__/prompt.test.js
@@ -9,7 +9,7 @@
 */
 'use strict';
 
-const Prompt = require('../Prompt');
+const Prompt = require('../prompt');
 let {KEYS} = require('../../constants');
 
 KEYS = Object.assign({}, KEYS, {
diff --git a/packages/jest-cli/src/lib/__tests__/scroll_list.test.js b/packages/jest-cli/src/lib/__tests__/scroll_list.test.js
index 23e4aa0a510a..dfb723e2fb14 100644
--- a/packages/jest-cli/src/lib/__tests__/scroll_list.test.js
+++ b/packages/jest-cli/src/lib/__tests__/scroll_list.test.js
@@ -1,4 +1,4 @@
-const scroll = require('../scrollList');
+const scroll = require('../scroll_list');
 
 it('When offset is -1', () => {
   expect(scroll(25, {max: 10, offset: -1})).toEqual({
diff --git a/packages/jest-cli/src/lib/__tests__/setState.js b/packages/jest-cli/src/lib/__tests__/set_state.js
similarity index 100%
rename from packages/jest-cli/src/lib/__tests__/setState.js
rename to packages/jest-cli/src/lib/__tests__/set_state.js
diff --git a/packages/jest-cli/src/lib/__tests__/validate_pattern.test.js b/packages/jest-cli/src/lib/__tests__/validate_pattern.test.js
index 24b651eb6e70..5a6d22152c14 100644
--- a/packages/jest-cli/src/lib/__tests__/validate_pattern.test.js
+++ b/packages/jest-cli/src/lib/__tests__/validate_pattern.test.js
@@ -9,7 +9,7 @@
  */
 'use strict';
 
-const validatePattern = require('../validatePattern');
+const validatePattern = require('../validate_pattern');
 
 describe('validate pattern function', () => {
   it('without passed args returns true', () => {
diff --git a/packages/jest-cli/src/lib/BufferedConsole.js b/packages/jest-cli/src/lib/buffered_console.js
similarity index 100%
rename from packages/jest-cli/src/lib/BufferedConsole.js
rename to packages/jest-cli/src/lib/buffered_console.js
diff --git a/packages/jest-cli/src/lib/createContext.js b/packages/jest-cli/src/lib/create_context.js
similarity index 100%
rename from packages/jest-cli/src/lib/createContext.js
rename to packages/jest-cli/src/lib/create_context.js
diff --git a/packages/jest-cli/src/lib/formatTestNameByPattern.js b/packages/jest-cli/src/lib/format_test_name_by_pattern.js
similarity index 100%
rename from packages/jest-cli/src/lib/formatTestNameByPattern.js
rename to packages/jest-cli/src/lib/format_test_name_by_pattern.js
diff --git a/packages/jest-cli/src/lib/getMaxWorkers.js b/packages/jest-cli/src/lib/get_max_workers.js
similarity index 100%
rename from packages/jest-cli/src/lib/getMaxWorkers.js
rename to packages/jest-cli/src/lib/get_max_workers.js
diff --git a/packages/jest-cli/src/lib/getTestPathPattern.js b/packages/jest-cli/src/lib/get_test_path_pattern.js
similarity index 94%
rename from packages/jest-cli/src/lib/getTestPathPattern.js
rename to packages/jest-cli/src/lib/get_test_path_pattern.js
index 1ce1a4402699..c6cf3505f960 100644
--- a/packages/jest-cli/src/lib/getTestPathPattern.js
+++ b/packages/jest-cli/src/lib/get_test_path_pattern.js
@@ -9,11 +9,11 @@
  */
 
 import type {Argv} from 'types/Argv';
-import type {TestSelectionConfig} from '../SearchSource';
+import type {TestSelectionConfig} from '../search_source';
 
 import {clearLine} from 'jest-util';
 import chalk from 'chalk';
-import validatePattern from './validatePattern';
+import validatePattern from './validate_pattern';
 
 const DEFAULT_PATTERN_INFO = {
   input: '',
diff --git a/packages/jest-cli/src/lib/handleDeprecationWarnings.js b/packages/jest-cli/src/lib/handle_deprecation_warnings.js
similarity index 100%
rename from packages/jest-cli/src/lib/handleDeprecationWarnings.js
rename to packages/jest-cli/src/lib/handle_deprecation_warnings.js
diff --git a/packages/jest-cli/src/lib/isValidPath.js b/packages/jest-cli/src/lib/is_valid_path.js
similarity index 100%
rename from packages/jest-cli/src/lib/isValidPath.js
rename to packages/jest-cli/src/lib/is_valid_path.js
diff --git a/packages/jest-cli/src/lib/logDebugMessages.js b/packages/jest-cli/src/lib/log_debug_messages.js
similarity index 100%
rename from packages/jest-cli/src/lib/logDebugMessages.js
rename to packages/jest-cli/src/lib/log_debug_messages.js
diff --git a/packages/jest-cli/src/lib/patternModeHelpers.js b/packages/jest-cli/src/lib/pattern_mode_helpers.js
similarity index 98%
rename from packages/jest-cli/src/lib/patternModeHelpers.js
rename to packages/jest-cli/src/lib/pattern_mode_helpers.js
index 82de807d6c4a..735ef326f330 100644
--- a/packages/jest-cli/src/lib/patternModeHelpers.js
+++ b/packages/jest-cli/src/lib/pattern_mode_helpers.js
@@ -13,7 +13,7 @@
 import chalk from 'chalk';
 import ansiEscapes from 'ansi-escapes';
 import stringLength from 'string-length';
-import Prompt from './Prompt';
+import Prompt from './prompt';
 
 const pluralize = (count: number, text: string) =>
   count === 1 ? text : text + 's';
diff --git a/packages/jest-cli/src/lib/Prompt.js b/packages/jest-cli/src/lib/prompt.js
similarity index 98%
rename from packages/jest-cli/src/lib/Prompt.js
rename to packages/jest-cli/src/lib/prompt.js
index d1e48f415863..5178fd50dec2 100644
--- a/packages/jest-cli/src/lib/Prompt.js
+++ b/packages/jest-cli/src/lib/prompt.js
@@ -8,7 +8,7 @@
  * @flow
  */
 
-import type {ScrollOptions} from './scrollList';
+import type {ScrollOptions} from './scroll_list';
 
 import {KEYS} from '../constants';
 
diff --git a/packages/jest-cli/src/lib/scrollList.js b/packages/jest-cli/src/lib/scroll_list.js
similarity index 100%
rename from packages/jest-cli/src/lib/scrollList.js
rename to packages/jest-cli/src/lib/scroll_list.js
diff --git a/packages/jest-cli/src/lib/terminalUtils.js b/packages/jest-cli/src/lib/terminal_utils.js
similarity index 100%
rename from packages/jest-cli/src/lib/terminalUtils.js
rename to packages/jest-cli/src/lib/terminal_utils.js
diff --git a/packages/jest-cli/src/lib/updateArgv.js b/packages/jest-cli/src/lib/update_argv.js
similarity index 95%
rename from packages/jest-cli/src/lib/updateArgv.js
rename to packages/jest-cli/src/lib/update_argv.js
index 969887c3d89e..0a16d7f35f3d 100644
--- a/packages/jest-cli/src/lib/updateArgv.js
+++ b/packages/jest-cli/src/lib/update_argv.js
@@ -10,7 +10,7 @@
 
 import type {Argv} from 'types/Argv';
 
-import getTestPathPattern from './getTestPathPattern';
+import getTestPathPattern from './get_test_path_pattern';
 
 type Options = {|
   testNamePattern?: string,
diff --git a/packages/jest-cli/src/lib/validatePattern.js b/packages/jest-cli/src/lib/validate_pattern.js
similarity index 100%
rename from packages/jest-cli/src/lib/validatePattern.js
rename to packages/jest-cli/src/lib/validate_pattern.js
diff --git a/packages/jest-cli/src/PatternPrompt.js b/packages/jest-cli/src/pattern_prompt.js
similarity index 95%
rename from packages/jest-cli/src/PatternPrompt.js
rename to packages/jest-cli/src/pattern_prompt.js
index 19a2a0ced922..3a58ffa199e2 100644
--- a/packages/jest-cli/src/PatternPrompt.js
+++ b/packages/jest-cli/src/pattern_prompt.js
@@ -10,11 +10,11 @@
 
 'use strict';
 
-import type {ScrollOptions} from './lib/scrollList';
+import type {ScrollOptions} from './lib/scroll_list';
 
 import chalk from 'chalk';
 import ansiEscapes from 'ansi-escapes';
-import Prompt from './lib/Prompt';
+import Prompt from './lib/prompt';
 
 const usage = (entity: string) =>
   `\n${chalk.bold('Pattern Mode Usage')}\n` +
diff --git a/packages/jest-cli/src/preRunMessage.js b/packages/jest-cli/src/pre_run_message.js
similarity index 100%
rename from packages/jest-cli/src/preRunMessage.js
rename to packages/jest-cli/src/pre_run_message.js
diff --git a/packages/jest-cli/src/ReporterDispatcher.js b/packages/jest-cli/src/reporter_dispatcher.js
similarity index 100%
rename from packages/jest-cli/src/ReporterDispatcher.js
rename to packages/jest-cli/src/reporter_dispatcher.js
diff --git a/packages/jest-cli/src/reporters/__tests__/coverage_reporter.test.js b/packages/jest-cli/src/reporters/__tests__/coverage_reporter.test.js
index 1b4ec241352d..09553bd94309 100644
--- a/packages/jest-cli/src/reporters/__tests__/coverage_reporter.test.js
+++ b/packages/jest-cli/src/reporters/__tests__/coverage_reporter.test.js
@@ -25,7 +25,7 @@ beforeEach(() => {
     write: jest.fn(),
   }));
 
-  CoverageReporter = require('../CoverageReporter');
+  CoverageReporter = require('../coverage_reporter');
   libCoverage = require('istanbul-lib-coverage');
   libSourceMaps = require('istanbul-lib-source-maps');
 });
diff --git a/packages/jest-cli/src/reporters/__tests__/coverage_worker.test.js b/packages/jest-cli/src/reporters/__tests__/coverage_worker.test.js
index a8ddf35655c7..6bc082d4a38c 100644
--- a/packages/jest-cli/src/reporters/__tests__/coverage_worker.test.js
+++ b/packages/jest-cli/src/reporters/__tests__/coverage_worker.test.js
@@ -8,7 +8,7 @@
 
 'use strict';
 
-jest.mock('fs').mock('../../generateEmptyCoverage');
+jest.mock('fs').mock('../../generate_empty_coverage');
 
 const globalConfig = {collectCoverage: true};
 const config = {};
@@ -22,8 +22,8 @@ beforeEach(() => {
   jest.resetModules();
 
   fs = require('fs');
-  generateEmptyCoverage = require('../../generateEmptyCoverage');
-  worker = require('../CoverageWorker');
+  generateEmptyCoverage = require('../../generate_empty_coverage');
+  worker = require('../coverage_worker');
 });
 
 test('resolves to the result of generateEmptyCoverage upon success', () => {
diff --git a/packages/jest-cli/src/reporters/__tests__/verbose_reporter.test.js b/packages/jest-cli/src/reporters/__tests__/verbose_reporter.test.js
index 9bd151af2169..27669b73a9f0 100644
--- a/packages/jest-cli/src/reporters/__tests__/verbose_reporter.test.js
+++ b/packages/jest-cli/src/reporters/__tests__/verbose_reporter.test.js
@@ -12,7 +12,7 @@ const wrap = obj => ({suites: obj, tests: [], title: ''});
 let groupTestsBySuites;
 
 beforeEach(() => {
-  groupTestsBySuites = require('../VerboseReporter').groupTestsBySuites;
+  groupTestsBySuites = require('../verbose_reporter').groupTestsBySuites;
 });
 
 describe('groupTestsBySuites', () => {
diff --git a/packages/jest-cli/src/reporters/BaseReporter.js b/packages/jest-cli/src/reporters/base_reporter.js
similarity index 96%
rename from packages/jest-cli/src/reporters/BaseReporter.js
rename to packages/jest-cli/src/reporters/base_reporter.js
index 27c14dd8452e..9716acb3650e 100644
--- a/packages/jest-cli/src/reporters/BaseReporter.js
+++ b/packages/jest-cli/src/reporters/base_reporter.js
@@ -13,7 +13,7 @@ import type {Context} from 'types/Context';
 import type {Test} from 'types/TestRunner';
 import type {ReporterOnStartOptions} from 'types/Reporters';
 
-import preRunMessage from '../preRunMessage';
+import preRunMessage from '../pre_run_message';
 
 class BaseReporter {
   _error: ?Error;
diff --git a/packages/jest-cli/src/reporters/CoverageReporter.js b/packages/jest-cli/src/reporters/coverage_reporter.js
similarity index 98%
rename from packages/jest-cli/src/reporters/CoverageReporter.js
rename to packages/jest-cli/src/reporters/coverage_reporter.js
index b9077f0c8ca0..23b6f6dd2708 100644
--- a/packages/jest-cli/src/reporters/CoverageReporter.js
+++ b/packages/jest-cli/src/reporters/coverage_reporter.js
@@ -30,8 +30,8 @@ import istanbulCoverage from 'istanbul-lib-coverage';
 import libSourceMaps from 'istanbul-lib-source-maps';
 import pify from 'pify';
 import workerFarm from 'worker-farm';
-import BaseReporter from './BaseReporter';
-import CoverageWorker from './CoverageWorker';
+import BaseReporter from './base_reporter';
+import CoverageWorker from './coverage_worker';
 
 const FAIL_COLOR = chalk.bold.red;
 const RUNNING_TEST_COLOR = chalk.bold.dim;
@@ -153,7 +153,7 @@ class CoverageReporter extends BaseReporter {
           maxConcurrentWorkers: this._maxWorkers,
           maxRetries: 2,
         },
-        require.resolve('./CoverageWorker'),
+        require.resolve('./coverage_worker'),
       );
       worker = pify(farm);
     }
diff --git a/packages/jest-cli/src/reporters/CoverageWorker.js b/packages/jest-cli/src/reporters/coverage_worker.js
similarity index 95%
rename from packages/jest-cli/src/reporters/CoverageWorker.js
rename to packages/jest-cli/src/reporters/coverage_worker.js
index 75e413f9b134..25ef877458ba 100644
--- a/packages/jest-cli/src/reporters/CoverageWorker.js
+++ b/packages/jest-cli/src/reporters/coverage_worker.js
@@ -12,7 +12,7 @@ import type {GlobalConfig, ProjectConfig, Path} from 'types/Config';
 import type {SerializableError} from 'types/TestResult';
 
 import fs from 'fs';
-import generateEmptyCoverage from '../generateEmptyCoverage';
+import generateEmptyCoverage from '../generate_empty_coverage';
 
 type CoverageWorkerData = {|
   globalConfig: GlobalConfig,
diff --git a/packages/jest-cli/src/reporters/DefaultReporter.js b/packages/jest-cli/src/reporters/default_reporter.js
similarity index 96%
rename from packages/jest-cli/src/reporters/DefaultReporter.js
rename to packages/jest-cli/src/reporters/default_reporter.js
index ab112da7adb5..000a52aab914 100644
--- a/packages/jest-cli/src/reporters/DefaultReporter.js
+++ b/packages/jest-cli/src/reporters/default_reporter.js
@@ -18,10 +18,10 @@ import type {ReporterOnStartOptions} from 'types/Reporters';
 import {clearLine} from 'jest-util';
 import chalk from 'chalk';
 import isCI from 'is-ci';
-import BaseReporter from './BaseReporter';
-import Status from './Status';
-import getConsoleOutput from './getConsoleOutput';
-import getResultHeader from './getResultHeader';
+import BaseReporter from './base_reporter';
+import Status from './status';
+import getConsoleOutput from './get_console_output';
+import getResultHeader from './get_result_header';
 
 type write = (chunk: string, enc?: any, cb?: () => void) => boolean;
 type FlushBufferedOutput = () => void;
diff --git a/packages/jest-cli/src/reporters/getConsoleOutput.js b/packages/jest-cli/src/reporters/get_console_output.js
similarity index 100%
rename from packages/jest-cli/src/reporters/getConsoleOutput.js
rename to packages/jest-cli/src/reporters/get_console_output.js
diff --git a/packages/jest-cli/src/reporters/getResultHeader.js b/packages/jest-cli/src/reporters/get_result_header.js
similarity index 100%
rename from packages/jest-cli/src/reporters/getResultHeader.js
rename to packages/jest-cli/src/reporters/get_result_header.js
diff --git a/packages/jest-cli/src/reporters/NotifyReporter.js b/packages/jest-cli/src/reporters/notify_reporter.js
similarity index 98%
rename from packages/jest-cli/src/reporters/NotifyReporter.js
rename to packages/jest-cli/src/reporters/notify_reporter.js
index 5deb6603327b..cfa8c589fcd2 100644
--- a/packages/jest-cli/src/reporters/NotifyReporter.js
+++ b/packages/jest-cli/src/reporters/notify_reporter.js
@@ -14,7 +14,7 @@ import type {Context} from 'types/Context';
 import path from 'path';
 import util from 'util';
 import notifier from 'node-notifier';
-import BaseReporter from './BaseReporter';
+import BaseReporter from './base_reporter';
 
 const isDarwin = process.platform === 'darwin';
 
diff --git a/packages/jest-cli/src/reporters/Status.js b/packages/jest-cli/src/reporters/status.js
similarity index 100%
rename from packages/jest-cli/src/reporters/Status.js
rename to packages/jest-cli/src/reporters/status.js
diff --git a/packages/jest-cli/src/reporters/SummaryReporter.js b/packages/jest-cli/src/reporters/summary_reporter.js
similarity index 97%
rename from packages/jest-cli/src/reporters/SummaryReporter.js
rename to packages/jest-cli/src/reporters/summary_reporter.js
index 215c11a9f6ae..2e6e0cad8fb4 100644
--- a/packages/jest-cli/src/reporters/SummaryReporter.js
+++ b/packages/jest-cli/src/reporters/summary_reporter.js
@@ -12,13 +12,13 @@ import type {AggregatedResult, SnapshotSummary} from 'types/TestResult';
 import type {GlobalConfig} from 'types/Config';
 import type {Context} from 'types/Context';
 import type {ReporterOnStartOptions} from 'types/Reporters';
-import type {TestRunnerOptions} from '../TestRunner';
-import type {TestSelectionConfig} from '../SearchSource';
+import type {TestRunnerOptions} from '../test_runner';
+import type {TestSelectionConfig} from '../search_source';
 
 import chalk from 'chalk';
-import BaseReporter from './BaseReporter';
+import BaseReporter from './base_reporter';
 import {getSummary, pluralize} from './utils';
-import getResultHeader from './getResultHeader';
+import getResultHeader from './get_result_header';
 
 const ARROW = ' \u203A ';
 const FAIL_COLOR = chalk.bold.red;
diff --git a/packages/jest-cli/src/reporters/VerboseReporter.js b/packages/jest-cli/src/reporters/verbose_reporter.js
similarity index 98%
rename from packages/jest-cli/src/reporters/VerboseReporter.js
rename to packages/jest-cli/src/reporters/verbose_reporter.js
index 0b27d48c8454..9d0012a1908c 100644
--- a/packages/jest-cli/src/reporters/VerboseReporter.js
+++ b/packages/jest-cli/src/reporters/verbose_reporter.js
@@ -19,7 +19,7 @@ import type {Test} from 'types/TestRunner';
 
 import chalk from 'chalk';
 import {ICONS} from '../constants';
-import DefaultReporter from './DefaultReporter';
+import DefaultReporter from './default_reporter';
 
 class VerboseReporter extends DefaultReporter {
   _globalConfig: GlobalConfig;
diff --git a/packages/jest-cli/src/runJest.js b/packages/jest-cli/src/run_jest.js
similarity index 94%
rename from packages/jest-cli/src/runJest.js
rename to packages/jest-cli/src/run_jest.js
index 8f3f11e6c0b3..66b4266d5227 100644
--- a/packages/jest-cli/src/runJest.js
+++ b/packages/jest-cli/src/run_jest.js
@@ -11,21 +11,21 @@
 import type {Argv} from 'types/Argv';
 import type {Context} from 'types/Context';
 import type {GlobalConfig} from 'types/Config';
-import type {TestSelectionConfig} from './SearchSource';
+import type {TestSelectionConfig} from './search_source';
 import type {AggregatedResult} from 'types/TestResult';
-import type TestWatcher from './TestWatcher';
+import type TestWatcher from './test_watcher';
 
 import path from 'path';
 import {Console, formatTestResults} from 'jest-util';
 import chalk from 'chalk';
 import fs from 'graceful-fs';
-import getMaxWorkers from './lib/getMaxWorkers';
-import getTestPathPattern from './lib/getTestPathPattern';
-import SearchSource from './SearchSource';
-import updateArgv from './lib/updateArgv';
-import TestRunner from './TestRunner';
-import TestSequencer from './TestSequencer';
-import {makeEmptyAggregatedTestResult} from './testResultHelpers';
+import getMaxWorkers from './lib/get_max_workers';
+import getTestPathPattern from './lib/get_test_path_pattern';
+import SearchSource from './search_source';
+import updateArgv from './lib/update_argv';
+import TestRunner from './test_runner';
+import TestSequencer from './test_sequencer';
+import {makeEmptyAggregatedTestResult} from './test_result_helpers';
 
 const setConfig = (contexts, newConfig) =>
   contexts.forEach(
diff --git a/packages/jest-cli/src/runTest.js b/packages/jest-cli/src/run_test.js
similarity index 97%
rename from packages/jest-cli/src/runTest.js
rename to packages/jest-cli/src/run_test.js
index a7f47d1a8af4..fd90b5f2611b 100644
--- a/packages/jest-cli/src/runTest.js
+++ b/packages/jest-cli/src/run_test.js
@@ -19,8 +19,8 @@ import fs from 'fs';
 import {Console, NullConsole, setGlobal} from 'jest-util';
 import {getTestEnvironment} from 'jest-config';
 import docblock from 'jest-docblock';
-import BufferedConsole from './lib/BufferedConsole';
-import getConsoleOutput from './reporters/getConsoleOutput';
+import BufferedConsole from './lib/buffered_console';
+import getConsoleOutput from './reporters/get_console_output';
 
 function runTest(
   path: Path,
diff --git a/packages/jest-cli/src/SearchSource.js b/packages/jest-cli/src/search_source.js
similarity index 100%
rename from packages/jest-cli/src/SearchSource.js
rename to packages/jest-cli/src/search_source.js
diff --git a/packages/jest-cli/src/TestNamePatternPrompt.js b/packages/jest-cli/src/test_name_pattern_prompt.js
similarity index 88%
rename from packages/jest-cli/src/TestNamePatternPrompt.js
rename to packages/jest-cli/src/test_name_pattern_prompt.js
index 4a9c7b01fd98..e614e1725e00 100644
--- a/packages/jest-cli/src/TestNamePatternPrompt.js
+++ b/packages/jest-cli/src/test_name_pattern_prompt.js
@@ -10,12 +10,12 @@
 
 import type {TestResult} from 'types/TestResult';
 import chalk from 'chalk';
-import type {ScrollOptions} from './lib/scrollList';
+import type {ScrollOptions} from './lib/scroll_list';
 
-import scroll from './lib/scrollList';
-import {getTerminalWidth} from './lib/terminalUtils';
-import Prompt from './lib/Prompt';
-import formatTestNameByPattern from './lib/formatTestNameByPattern';
+import scroll from './lib/scroll_list';
+import {getTerminalWidth} from './lib/terminal_utils';
+import Prompt from './lib/prompt';
+import formatTestNameByPattern from './lib/format_test_name_by_pattern';
 import {
   formatTypeaheadSelection,
   printMore,
@@ -24,8 +24,8 @@ import {
   printRestoredPatternCaret,
   printStartTyping,
   printTypeaheadItem,
-} from './lib/patternModeHelpers';
-import PatternPrompt from './PatternPrompt';
+} from './lib/pattern_mode_helpers';
+import PatternPrompt from './pattern_prompt';
 
 module.exports = class TestNamePatternPrompt extends PatternPrompt {
   _cachedTestResults: Array<TestResult>;
diff --git a/packages/jest-cli/src/TestPathPatternPrompt.js b/packages/jest-cli/src/test_path_pattern_prompt.js
similarity index 90%
rename from packages/jest-cli/src/TestPathPatternPrompt.js
rename to packages/jest-cli/src/test_path_pattern_prompt.js
index 65137eaa6f71..9934bc95cd07 100644
--- a/packages/jest-cli/src/TestPathPatternPrompt.js
+++ b/packages/jest-cli/src/test_path_pattern_prompt.js
@@ -10,17 +10,17 @@
 
 import type {Context} from 'types/Context';
 import type {Test} from 'types/TestRunner';
-import type {ScrollOptions} from './lib/scrollList';
+import type {ScrollOptions} from './lib/scroll_list';
 // eslint-disable-next-line import/default
-import type SearchSource from './SearchSource';
+import type SearchSource from './search_source';
 
 import chalk from 'chalk';
 import stringLength from 'string-length';
-import scroll from './lib/scrollList';
-import {getTerminalWidth} from './lib/terminalUtils';
+import scroll from './lib/scroll_list';
+import {getTerminalWidth} from './lib/terminal_utils';
 import highlight from './lib/highlight';
 import {trimAndFormatPath} from './reporters/utils';
-import Prompt from './lib/Prompt';
+import Prompt from './lib/prompt';
 import {
   formatTypeaheadSelection,
   printMore,
@@ -29,8 +29,8 @@ import {
   printRestoredPatternCaret,
   printStartTyping,
   printTypeaheadItem,
-} from './lib/patternModeHelpers';
-import PatternPrompt from './PatternPrompt';
+} from './lib/pattern_mode_helpers';
+import PatternPrompt from './pattern_prompt';
 
 type SearchSources = Array<{|
   context: Context,
diff --git a/packages/jest-cli/src/testResultHelpers.js b/packages/jest-cli/src/test_result_helpers.js
similarity index 100%
rename from packages/jest-cli/src/testResultHelpers.js
rename to packages/jest-cli/src/test_result_helpers.js
diff --git a/packages/jest-cli/src/TestRunner.js b/packages/jest-cli/src/test_runner.js
similarity index 95%
rename from packages/jest-cli/src/TestRunner.js
rename to packages/jest-cli/src/test_runner.js
index 3fa0665bd0d3..d4ded03b63c8 100644
--- a/packages/jest-cli/src/TestRunner.js
+++ b/packages/jest-cli/src/test_runner.js
@@ -16,26 +16,26 @@ import type {
 import type {GlobalConfig, ReporterConfig} from 'types/Config';
 import type {Context} from 'types/Context';
 import type {Reporter, Test} from 'types/TestRunner';
-import type {TestSelectionConfig} from './SearchSource';
+import type {TestSelectionConfig} from './search_source';
 
 import {formatExecError} from 'jest-message-util';
 import {
   addResult,
   buildFailureTestResult,
   makeEmptyAggregatedTestResult,
-} from './testResultHelpers';
+} from './test_result_helpers';
 import snapshot from 'jest-snapshot';
 import pify from 'pify';
 import throat from 'throat';
 import workerFarm from 'worker-farm';
-import DefaultReporter from './reporters/DefaultReporter';
-import NotifyReporter from './reporters/NotifyReporter';
-import SummaryReporter from './reporters/SummaryReporter';
-import VerboseReporter from './reporters/VerboseReporter';
-import runTest from './runTest';
-import TestWatcher from './TestWatcher';
-import CoverageReporter from './reporters/CoverageReporter';
-import ReporterDispatcher from './ReporterDispatcher';
+import DefaultReporter from './reporters/default_reporter';
+import NotifyReporter from './reporters/notify_reporter';
+import SummaryReporter from './reporters/summary_reporter';
+import VerboseReporter from './reporters/verbose_reporter';
+import runTest from './run_test';
+import TestWatcher from './test_watcher';
+import CoverageReporter from './reporters/coverage_reporter';
+import ReporterDispatcher from './reporter_dispatcher';
 
 const SLOW_TEST_TIME = 3000;
 
@@ -57,7 +57,7 @@ export type TestRunnerOptions = {|
 type OnTestFailure = (test: Test, err: TestError) => void;
 type OnTestSuccess = (test: Test, result: TestResult) => Promise<*>;
 
-const TEST_WORKER_PATH = require.resolve('./TestWorker');
+const TEST_WORKER_PATH = require.resolve('./test_worker');
 
 class TestRunner {
   _globalConfig: GlobalConfig;
diff --git a/packages/jest-cli/src/TestSequencer.js b/packages/jest-cli/src/test_sequencer.js
similarity index 100%
rename from packages/jest-cli/src/TestSequencer.js
rename to packages/jest-cli/src/test_sequencer.js
diff --git a/packages/jest-cli/src/TestWatcher.js b/packages/jest-cli/src/test_watcher.js
similarity index 100%
rename from packages/jest-cli/src/TestWatcher.js
rename to packages/jest-cli/src/test_watcher.js
diff --git a/packages/jest-cli/src/TestWorker.js b/packages/jest-cli/src/test_worker.js
similarity index 98%
rename from packages/jest-cli/src/TestWorker.js
rename to packages/jest-cli/src/test_worker.js
index ff89dd1575f3..0a03be90baab 100644
--- a/packages/jest-cli/src/TestWorker.js
+++ b/packages/jest-cli/src/test_worker.js
@@ -22,7 +22,7 @@ process.on('uncaughtException', err => {
 import {ModuleMap} from 'jest-haste-map';
 import {separateMessageFromStack} from 'jest-message-util';
 import Runtime from 'jest-runtime';
-import runTest from './runTest';
+import runTest from './run_test';
 
 type WorkerData = {|
   config: ProjectConfig,
diff --git a/packages/jest-cli/src/watch.js b/packages/jest-cli/src/watch.js
index 26a9156e78b6..b98c94f151c7 100644
--- a/packages/jest-cli/src/watch.js
+++ b/packages/jest-cli/src/watch.js
@@ -17,16 +17,16 @@ import chalk from 'chalk';
 import {replacePathSepForRegex} from 'jest-regex-util';
 import HasteMap from 'jest-haste-map';
 import isCI from 'is-ci';
-import isValidPath from './lib/isValidPath';
-import preRunMessage from './preRunMessage';
-import createContext from './lib/createContext';
-import runJest from './runJest';
-import updateArgv from './lib/updateArgv';
-import SearchSource from './SearchSource';
-import TestWatcher from './TestWatcher';
-import Prompt from './lib/Prompt';
-import TestPathPatternPrompt from './TestPathPatternPrompt';
-import TestNamePatternPrompt from './TestNamePatternPrompt';
+import isValidPath from './lib/is_valid_path';
+import preRunMessage from './pre_run_message';
+import createContext from './lib/create_context';
+import runJest from './run_jest';
+import updateArgv from './lib/update_argv';
+import SearchSource from './search_source';
+import TestWatcher from './test_watcher';
+import Prompt from './lib/prompt';
+import TestPathPatternPrompt from './test_path_pattern_prompt';
+import TestNamePatternPrompt from './test_name_pattern_prompt';
 import {KEYS, CLEAR} from './constants';
 
 const isInteractive = process.stdout.isTTY && !isCI;
diff --git a/packages/jest-config/src/__tests__/normalize.test.js b/packages/jest-config/src/__tests__/normalize.test.js
index 6e61a522e859..c26c291df90e 100644
--- a/packages/jest-config/src/__tests__/normalize.test.js
+++ b/packages/jest-config/src/__tests__/normalize.test.js
@@ -272,7 +272,7 @@ describe('haste', () => {
     const {options} = normalize(
       {
         haste: {
-          hasteImplModulePath: '<rootDir>/hasteImpl.js',
+          hasteImplModulePath: '<rootDir>/haste_impl.js',
         },
         rootDir: '/root/',
       },
@@ -280,7 +280,7 @@ describe('haste', () => {
     );
 
     expect(options.haste).toEqual({
-      hasteImplModulePath: '/root/hasteImpl.js',
+      hasteImplModulePath: '/root/haste_impl.js',
     });
   });
 });
diff --git a/packages/jest-config/src/valid_config.js b/packages/jest-config/src/valid_config.js
index 3feb3fa07a71..a8c6c0eeea60 100644
--- a/packages/jest-config/src/valid_config.js
+++ b/packages/jest-config/src/valid_config.js
@@ -67,7 +67,7 @@ module.exports = ({
   rootDir: '/',
   roots: ['<rootDir>'],
   setupFiles: ['<rootDir>/setup.js'],
-  setupTestFrameworkScriptFile: '<rootDir>/testSetupFile.js',
+  setupTestFrameworkScriptFile: '<rootDir>/test_setup_file.js',
   silent: true,
   snapshotSerializers: ['my-serializer-module'],
   testEnvironment: 'jest-environment-jsdom',
diff --git a/packages/jest-editor-support/src/__tests__/parsers/babylon_parser.test.js b/packages/jest-editor-support/src/__tests__/parsers/babylon_parser.test.js
index 73d6c7b325e0..63940a4220e2 100644
--- a/packages/jest-editor-support/src/__tests__/parsers/babylon_parser.test.js
+++ b/packages/jest-editor-support/src/__tests__/parsers/babylon_parser.test.js
@@ -9,6 +9,6 @@
 'use strict';
 
 const {parse} = require('../../parsers/babylon_parser');
-const {parserTests} = require('../../../../../fixtures/parserTests');
+const {parserTests} = require('../../../../../fixtures/parser_tests');
 
 parserTests(parse);
diff --git a/packages/jest-haste-map/src/__tests__/hasteImpl.js b/packages/jest-haste-map/src/__tests__/haste_impl.js
similarity index 100%
rename from packages/jest-haste-map/src/__tests__/hasteImpl.js
rename to packages/jest-haste-map/src/__tests__/haste_impl.js
diff --git a/packages/jest-haste-map/src/__tests__/worker.test.js b/packages/jest-haste-map/src/__tests__/worker.test.js
index 7287ef656638..867c14578610 100644
--- a/packages/jest-haste-map/src/__tests__/worker.test.js
+++ b/packages/jest-haste-map/src/__tests__/worker.test.js
@@ -104,7 +104,7 @@ describe('worker', () => {
     worker(
       {
         filePath: '/fruits/strawberry.js',
-        hasteImplModulePath: path.resolve(__dirname, 'hasteImpl.js'),
+        hasteImplModulePath: path.resolve(__dirname, 'haste_impl.js'),
       },
       callback,
     );
diff --git a/packages/jest-haste-map/src/index.js b/packages/jest-haste-map/src/index.js
index 571285386e68..d313c1ff0e4c 100644
--- a/packages/jest-haste-map/src/index.js
+++ b/packages/jest-haste-map/src/index.js
@@ -156,7 +156,7 @@ const getWhiteList = (list: ?Array<string>): ?RegExp => {
  * };
  *
  * // Modules can be targeted to a specific platform based on the file name.
- * // Example: Platform.ios.js and Platform.android.js will both map to the same
+ * // Example: platform.ios.js and Platform.android.js will both map to the same
  * // `Platform` module. The platform should be specified during resolution.
  * type ModuleMapItem = {[platform: string]: ModuleMetaData};
  *
diff --git a/packages/jest-jasmine2/src/__tests__/integration/lifecycle-hooks-test.js b/packages/jest-jasmine2/src/__tests__/integration/lifecycle_hooks_test.js
similarity index 100%
rename from packages/jest-jasmine2/src/__tests__/integration/lifecycle-hooks-test.js
rename to packages/jest-jasmine2/src/__tests__/integration/lifecycle_hooks_test.js
diff --git a/packages/jest-runtime/src/__mocks__/createRuntime.js b/packages/jest-runtime/src/__mocks__/createRuntime.js
index bd544fe94a1b..8f3fe23f3a02 100644
--- a/packages/jest-runtime/src/__mocks__/createRuntime.js
+++ b/packages/jest-runtime/src/__mocks__/createRuntime.js
@@ -41,7 +41,7 @@ module.exports = function createRuntime(filename, config) {
         config.rootDir,
         'subdir2',
         'module_dir',
-        'moduleDirModule.js',
+        'module_dir_module.js',
       );
       return runtime;
     });
diff --git a/packages/jest-runtime/src/__tests__/NODE_PATH_dir/RegularModuleInNodePath.js b/packages/jest-runtime/src/__tests__/NODE_PATH_dir/regular_module_in_node_path.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/NODE_PATH_dir/RegularModuleInNodePath.js
rename to packages/jest-runtime/src/__tests__/NODE_PATH_dir/regular_module_in_node_path.js
diff --git a/packages/jest-runtime/src/__tests__/__snapshots__/script_transformer.test.js.snap b/packages/jest-runtime/src/__tests__/__snapshots__/script_transformer.test.js.snap
index f4311abae9c2..d2deb8aab43b 100644
--- a/packages/jest-runtime/src/__tests__/__snapshots__/script_transformer.test.js.snap
+++ b/packages/jest-runtime/src/__tests__/__snapshots__/script_transformer.test.js.snap
@@ -15,7 +15,7 @@ exports[`ScriptTransformer uses multiple preprocessors 1`] = `
           const TRANSFORMED = {
             filename: '/fruits/banana.js',
             script: 'module.exports = \\"banana\\";',
-            config: '{\\"cache\\":true,\\"cacheDirectory\\":\\"/cache/\\",\\"name\\":\\"test\\",\\"rootDir\\":\\"/\\",\\"transformIgnorePatterns\\":[\\"/node_modules/\\"],\\"transform\\":[[\\"^.+\\\\\\\\.js$\\",\\"test-preprocessor\\"],[\\"^.+\\\\\\\\.css$\\",\\"css-preprocessor\\"]]}',
+            config: '{\\"cache\\":true,\\"cacheDirectory\\":\\"/cache/\\",\\"name\\":\\"test\\",\\"rootDir\\":\\"/\\",\\"transformIgnorePatterns\\":[\\"/node_modules/\\"],\\"transform\\":[[\\"^.+\\\\\\\\.js$\\",\\"test_preprocessor\\"],[\\"^.+\\\\\\\\.css$\\",\\"css-preprocessor\\"]]}',
           };
         
 }});"
@@ -41,7 +41,7 @@ exports[`ScriptTransformer uses the supplied preprocessor 1`] = `
           const TRANSFORMED = {
             filename: '/fruits/banana.js',
             script: 'module.exports = \\"banana\\";',
-            config: '{\\"cache\\":true,\\"cacheDirectory\\":\\"/cache/\\",\\"name\\":\\"test\\",\\"rootDir\\":\\"/\\",\\"transformIgnorePatterns\\":[\\"/node_modules/\\"],\\"transform\\":[[\\"^.+\\\\\\\\.js$\\",\\"test-preprocessor\\"]]}',
+            config: '{\\"cache\\":true,\\"cacheDirectory\\":\\"/cache/\\",\\"name\\":\\"test\\",\\"rootDir\\":\\"/\\",\\"transformIgnorePatterns\\":[\\"/node_modules/\\"],\\"transform\\":[[\\"^.+\\\\\\\\.js$\\",\\"test_preprocessor\\"]]}',
           };
         
 }});"
diff --git a/packages/jest-runtime/src/__tests__/instrumentation.test.js b/packages/jest-runtime/src/__tests__/instrumentation.test.js
index f779a69b948e..6ec258a70362 100644
--- a/packages/jest-runtime/src/__tests__/instrumentation.test.js
+++ b/packages/jest-runtime/src/__tests__/instrumentation.test.js
@@ -16,7 +16,7 @@ const os = require('os');
 
 const FILE_PATH_TO_INSTRUMENT = path.resolve(
   __dirname,
-  './module_dir/to-be-instrumented.js',
+  './module_dir/to_be_instrumented.js',
 );
 
 it('instruments files', () => {
diff --git a/packages/jest-runtime/src/__tests__/module_dir/moduleDirectoryFile.js b/packages/jest-runtime/src/__tests__/module_dir/module_directory_file.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/module_dir/moduleDirectoryFile.js
rename to packages/jest-runtime/src/__tests__/module_dir/module_directory_file.js
diff --git a/packages/jest-runtime/src/__tests__/module_dir/to-be-instrumented.js b/packages/jest-runtime/src/__tests__/module_dir/to_be_instrumented.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/module_dir/to-be-instrumented.js
rename to packages/jest-runtime/src/__tests__/module_dir/to_be_instrumented.js
diff --git a/packages/jest-runtime/src/__tests__/runtime_environment.test.js b/packages/jest-runtime/src/__tests__/runtime_environment.test.js
index 0be8b2c7f0ad..96d1261165ee 100644
--- a/packages/jest-runtime/src/__tests__/runtime_environment.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_environment.test.js
@@ -34,7 +34,7 @@ describe('Runtime', () => {
         let hasThrown = false;
         const sum = runtime.requireModule(
           runtime.__mockRootPath,
-          './throwing-fn.js',
+          './throwing_fn.js',
         );
 
         try {
@@ -43,11 +43,11 @@ describe('Runtime', () => {
           hasThrown = true;
           if (process.platform === 'win32') {
             expect(err.stack).toMatch(
-              /^Error: throwing fn\s+at sum.+\\__tests__\\test_root\\throwing-fn.js:12:9/,
+              /^Error: throwing fn\s+at sum.+\\__tests__\\test_root\\throwing_fn.js:12:9/,
             );
           } else {
             expect(err.stack).toMatch(
-              /^Error: throwing fn\s+at sum.+\/__tests__\/test_root\/throwing-fn.js:12:9/,
+              /^Error: throwing fn\s+at sum.+\/__tests__\/test_root\/throwing_fn.js:12:9/,
             );
           }
         }
diff --git a/packages/jest-runtime/src/__tests__/runtime_internal_module.test.js b/packages/jest-runtime/src/__tests__/runtime_internal_module.test.js
index 044ed4ed5411..ad2ef46bfc1c 100644
--- a/packages/jest-runtime/src/__tests__/runtime_internal_module.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_internal_module.test.js
@@ -23,7 +23,7 @@ describe('Runtime', () => {
   describe('internalModule', () => {
     it('loads modules and applies transforms', () =>
       createRuntime(__filename, {
-        transform: {'^.+\\.js$': './test-preprocessor'},
+        transform: {'^.+\\.js$': './test_preprocessor'},
       }).then(runtime => {
         const modulePath = path.resolve(
           path.dirname(runtime.__mockRootPath),
@@ -36,7 +36,7 @@ describe('Runtime', () => {
 
     it('loads internal modules without applying transforms', () =>
       createRuntime(__filename, {
-        transform: {'^.+\\.js$': './test-preprocessor'},
+        transform: {'^.+\\.js$': './test_preprocessor'},
       }).then(runtime => {
         const modulePath = path.resolve(
           path.dirname(runtime.__mockRootPath),
diff --git a/packages/jest-runtime/src/__tests__/Runtime-jest-fn.js b/packages/jest-runtime/src/__tests__/runtime_jest_fn.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/Runtime-jest-fn.js
rename to packages/jest-runtime/src/__tests__/runtime_jest_fn.js
diff --git a/packages/jest-runtime/src/__tests__/runtime_module_directories.test.js b/packages/jest-runtime/src/__tests__/runtime_module_directories.test.js
index 830edf9601ae..6d049e3743b4 100644
--- a/packages/jest-runtime/src/__tests__/runtime_module_directories.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_module_directories.test.js
@@ -28,7 +28,7 @@ describe('Runtime', () => {
     }).then(runtime => {
       const exports = runtime.requireModule(
         runtime.__mockRootPath,
-        'moduleDirModule',
+        'module_dir_module',
       );
       expect(exports).toBeDefined();
     }));
@@ -47,11 +47,11 @@ describe('Runtime', () => {
   it('finds closest module from moduleDirectories', () =>
     createRuntime(__filename, {moduleDirectories}).then(runtime => {
       const exports = runtime.requireModule(
-        path.join(rootDir, 'subdir2', 'MyModule.js'),
-        'moduleDirModule',
+        path.join(rootDir, 'subdir2', 'my_module.js'),
+        'module_dir_module',
       );
       expect(exports.modulePath).toEqual(
-        'subdir2/module_dir/moduleDirModule.js',
+        'subdir2/module_dir/module_dir_module.js',
       );
     }));
 
diff --git a/packages/jest-runtime/src/__tests__/runtime_node_path.test.js b/packages/jest-runtime/src/__tests__/runtime_node_path.test.js
index e167d9b0b9fa..0ec0069890e4 100644
--- a/packages/jest-runtime/src/__tests__/runtime_node_path.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_node_path.test.js
@@ -31,7 +31,7 @@ describe('Runtime', () => {
     return createLocalRuntime(nodePath).then(runtime => {
       const exports = runtime.requireModuleOrMock(
         runtime.__mockRootPath,
-        'RegularModuleInNodePath',
+        'regular_module_in_node_path',
       );
       expect(exports).toBeDefined();
     });
@@ -42,7 +42,7 @@ describe('Runtime', () => {
     return createLocalRuntime(null, {modulePaths: [nodePath]}).then(runtime => {
       const exports = runtime.requireModuleOrMock(
         runtime.__mockRootPath,
-        'RegularModuleInNodePath',
+        'regular_module_in_node_path',
       );
       expect(exports).toBeDefined();
     });
@@ -54,7 +54,7 @@ describe('Runtime', () => {
     return createLocalRuntime(nodePath).then(runtime => {
       const exports = runtime.requireModuleOrMock(
         runtime.__mockRootPath,
-        'RegularModuleInNodePath',
+        'regular_module_in_node_path',
       );
       expect(exports).toBeDefined();
     });
@@ -67,11 +67,11 @@ describe('Runtime', () => {
       expect(() => {
         runtime.requireModuleOrMock(
           runtime.__mockRootPath,
-          'RegularModuleInNodePath',
+          'regular_module_in_node_path',
         );
       }).toThrow(
         new Error(
-          `Cannot find module 'RegularModuleInNodePath' from 'root.js'`,
+          `Cannot find module 'regular_module_in_node_path' from 'root.js'`,
         ),
       );
     });
diff --git a/packages/jest-runtime/src/__tests__/runtime_require_mock.test.js b/packages/jest-runtime/src/__tests__/runtime_require_mock.test.js
index fcc3dfc29716..508ab70936f5 100644
--- a/packages/jest-runtime/src/__tests__/runtime_require_mock.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_require_mock.test.js
@@ -149,15 +149,15 @@ describe('Runtime', () => {
         expect(console.warn).toBeCalled();
         const exports1 = runtime.requireMock(
           runtime.__mockRootPath,
-          './subdir1/MyModule',
+          './subdir1/my_module',
         );
-        expect(exports1.modulePath).toEqual('subdir1/__mocks__/MyModule.js');
+        expect(exports1.modulePath).toEqual('subdir1/__mocks__/my_module.js');
 
         const exports2 = runtime.requireMock(
           runtime.__mockRootPath,
-          './subdir2/MyModule',
+          './subdir2/my_module',
         );
-        expect(exports2.modulePath).toEqual('subdir2/__mocks__/MyModule.js');
+        expect(exports2.modulePath).toEqual('subdir2/__mocks__/my_module.js');
       });
     });
   });
diff --git a/packages/jest-runtime/src/__tests__/runtime_require_module.test.js b/packages/jest-runtime/src/__tests__/runtime_require_module.test.js
index 062680d4929f..382ad3432d29 100644
--- a/packages/jest-runtime/src/__tests__/runtime_require_module.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_require_module.test.js
@@ -258,7 +258,7 @@ describe('Runtime requireModule', () => {
     createRuntime(__filename).then(runtime => {
       const exports = runtime.requireModule(
         runtime.__mockRootPath,
-        './UTF8WithBOM.js',
+        './utf8_with_bom.js',
       );
       expect(exports).toBe('isModuleEncodedInUTF8WithBOM');
     }));
@@ -267,7 +267,7 @@ describe('Runtime requireModule', () => {
     createRuntime(__filename).then(runtime => {
       const exports = runtime.requireModule(
         runtime.__mockRootPath,
-        './UTF8WithBOM.json',
+        './utf8_with_bom.json',
       );
       expect(exports.isJSONModuleEncodedInUTF8WithBOM).toBe(true);
     }));
diff --git a/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock.test.js b/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock.test.js
index 4f9a2748c1d9..0191df7edba9 100644
--- a/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock.test.js
@@ -12,10 +12,10 @@
 const moduleNameMapper = {
   '\\.css$': '<rootDir>/__mocks__/ManuallyMocked',
   '^[./a-zA-Z0-9$_-]+\.png$': 'RelativeImageStub',
-  '^image![a-zA-Z0-9$_-]+$': 'GlobalImageStub',
+  '^image![a-zA-Z0-9$_-]+$': 'global_image_stub',
   mappedToDirectory: '<rootDir>/MyDirectoryModule',
   mappedToModule: '<rootDir>/TestModuleNameMapperResolution',
-  mappedToPath: '<rootDir>/GlobalImageStub.js',
+  mappedToPath: '<rootDir>/global_image_stub.js',
   'module/name/(.*)': '<rootDir>/mapped_module_$1.js',
 };
 
@@ -106,7 +106,7 @@ it('resolves mapped module names and unmocks them by default', () =>
   }).then(runtime => {
     let exports = runtime.requireModuleOrMock(
       runtime.__mockRootPath,
-      'image!not-really-a-module',
+      'image!not_really_a_module',
     );
     expect(exports.isGlobalImageStub).toBe(true);
 
diff --git a/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock_transitive_deps.test.js b/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock_transitive_deps.test.js
index ffab717d7eb7..a1e12cdf7ffc 100644
--- a/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock_transitive_deps.test.js
+++ b/packages/jest-runtime/src/__tests__/runtime_require_module_or_mock_transitive_deps.test.js
@@ -13,10 +13,10 @@ let createRuntime;
 
 const moduleNameMapper = {
   '^[./a-zA-Z0-9$_-]+\.png$': 'RelativeImageStub',
-  '^image![a-zA-Z0-9$_-]+$': 'GlobalImageStub',
+  '^image![a-zA-Z0-9$_-]+$': 'global_image_stub',
   '^testMapped/(.*)': '<rootDir>/mapped_dir/$1',
   mappedToDirectory: '<rootDir>/MyDirectoryModule',
-  mappedToPath: '<rootDir>/GlobalImageStub.js',
+  mappedToPath: '<rootDir>/global_image_stub.js',
   'module/name/(.*)': '<rootDir>/mapped_module_$1.js',
 };
 
@@ -47,7 +47,7 @@ describe('transitive dependencies', () => {
 
       const parentDep = runtime.requireModule(
         runtime.__mockRootPath,
-        './depOnMappedModule.js',
+        './dep_on_mapped_module.js',
       );
       expect(parentDep).toEqual({result: 'mocked_in_mapped'});
     }));
diff --git a/packages/jest-runtime/src/__tests__/script_transformer.test.js b/packages/jest-runtime/src/__tests__/script_transformer.test.js
index cc1971409f0e..c1c1b5d56a20 100644
--- a/packages/jest-runtime/src/__tests__/script_transformer.test.js
+++ b/packages/jest-runtime/src/__tests__/script_transformer.test.js
@@ -24,7 +24,7 @@ jest
   .mock('vm');
 
 jest.mock(
-  'test-preprocessor',
+  'test_preprocessor',
   () => {
     const escapeStrings = str => {
       return str.replace(/'/, `'`);
@@ -233,12 +233,12 @@ describe('ScriptTransformer', () => {
 
   it('uses the supplied preprocessor', () => {
     config = Object.assign(config, {
-      transform: [['^.+\\.js$', 'test-preprocessor']],
+      transform: [['^.+\\.js$', 'test_preprocessor']],
     });
     const scriptTransformer = new ScriptTransformer(config);
     scriptTransformer.transform('/fruits/banana.js', {});
 
-    expect(require('test-preprocessor').getCacheKey).toBeCalled();
+    expect(require('test_preprocessor').getCacheKey).toBeCalled();
 
     expect(vm.Script.mock.calls[0][0]).toMatchSnapshot();
 
@@ -250,7 +250,7 @@ describe('ScriptTransformer', () => {
   it('uses multiple preprocessors', () => {
     config = Object.assign(config, {
       transform: [
-        ['^.+\\.js$', 'test-preprocessor'],
+        ['^.+\\.js$', 'test_preprocessor'],
         ['^.+\\.css$', 'css-preprocessor'],
       ],
     });
@@ -259,7 +259,7 @@ describe('ScriptTransformer', () => {
     scriptTransformer.transform('/fruits/banana.js', {});
     scriptTransformer.transform('/styles/App.css', {});
 
-    expect(require('test-preprocessor').getCacheKey).toBeCalled();
+    expect(require('test_preprocessor').getCacheKey).toBeCalled();
     expect(require('css-preprocessor').getCacheKey).toBeCalled();
     expect(vm.Script.mock.calls[0][0]).toMatchSnapshot();
     expect(vm.Script.mock.calls[1][0]).toMatchSnapshot();
@@ -353,7 +353,7 @@ describe('ScriptTransformer', () => {
 
   it('reads values from the cache', () => {
     const transformConfig = Object.assign(config, {
-      transform: [['^.+\\.js$', 'test-preprocessor']],
+      transform: [['^.+\\.js$', 'test_preprocessor']],
     });
     let scriptTransformer = new ScriptTransformer(transformConfig);
     scriptTransformer.transform('/fruits/banana.js', {});
diff --git a/packages/jest-runtime/src/__tests__/test_root/depOnMappedModule.js b/packages/jest-runtime/src/__tests__/test_root/dep_on_mapped_module.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/depOnMappedModule.js
rename to packages/jest-runtime/src/__tests__/test_root/dep_on_mapped_module.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/GlobalImageStub.js b/packages/jest-runtime/src/__tests__/test_root/global_image_stub.js
similarity index 90%
rename from packages/jest-runtime/src/__tests__/test_root/GlobalImageStub.js
rename to packages/jest-runtime/src/__tests__/test_root/global_image_stub.js
index 0fd8277e653e..a07525a17a18 100644
--- a/packages/jest-runtime/src/__tests__/test_root/GlobalImageStub.js
+++ b/packages/jest-runtime/src/__tests__/test_root/global_image_stub.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree. An additional grant
  * of patent rights can be found in the PATENTS file in the same directory.
  *
- * @providesModule GlobalImageStub
+ * @providesModule global_image_stub
  */
 
 'use strict';
diff --git a/packages/jest-runtime/src/__tests__/test_root/module_dir/module_dir_module.js b/packages/jest-runtime/src/__tests__/test_root/module_dir/module_dir_module.js
new file mode 100644
index 000000000000..09bf7b994d9e
--- /dev/null
+++ b/packages/jest-runtime/src/__tests__/test_root/module_dir/module_dir_module.js
@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+'use strict';
+
+exports.modulePath = 'module_dir/module_dir_module.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root/platform/Platform.android.js b/packages/jest-runtime/src/__tests__/test_root/platform/platform.android.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/platform/Platform.android.js
rename to packages/jest-runtime/src/__tests__/test_root/platform/platform.android.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/platform/Platform.ios.js b/packages/jest-runtime/src/__tests__/test_root/platform/platform.ios.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/platform/Platform.ios.js
rename to packages/jest-runtime/src/__tests__/test_root/platform/platform.ios.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/platform/Platform.js b/packages/jest-runtime/src/__tests__/test_root/platform/platform.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/platform/Platform.js
rename to packages/jest-runtime/src/__tests__/test_root/platform/platform.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/platform/Platform.native.js b/packages/jest-runtime/src/__tests__/test_root/platform/platform.native.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/platform/Platform.native.js
rename to packages/jest-runtime/src/__tests__/test_root/platform/platform.native.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/root.js b/packages/jest-runtime/src/__tests__/test_root/root.js
index 4ec2d1328278..d05cb3713838 100644
--- a/packages/jest-runtime/src/__tests__/test_root/root.js
+++ b/packages/jest-runtime/src/__tests__/test_root/root.js
@@ -17,7 +17,7 @@ require('RegularModule');
 
 // We only care about the static analysis, not about the runtime.
 const lazyRequire = () => {
-  require('image!not-really-a-module');
+  require('image!not_really_a_module');
   require('cat.png');
   require('dog.png');
 };
diff --git a/packages/jest-runtime/src/__tests__/test_root/subdir2/module_dir/moduleDirModule.js b/packages/jest-runtime/src/__tests__/test_root/subdir2/module_dir/module_dir_module.js
similarity index 83%
rename from packages/jest-runtime/src/__tests__/test_root/subdir2/module_dir/moduleDirModule.js
rename to packages/jest-runtime/src/__tests__/test_root/subdir2/module_dir/module_dir_module.js
index b9f4e0a28d11..145796b83885 100644
--- a/packages/jest-runtime/src/__tests__/test_root/subdir2/module_dir/moduleDirModule.js
+++ b/packages/jest-runtime/src/__tests__/test_root/subdir2/module_dir/module_dir_module.js
@@ -8,4 +8,4 @@
 
 'use strict';
 
-exports.modulePath = 'subdir2/module_dir/moduleDirModule.js';
+exports.modulePath = 'subdir2/module_dir/module_dir_module.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root/test-preprocessor.js b/packages/jest-runtime/src/__tests__/test_root/test_preprocessor.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/test-preprocessor.js
rename to packages/jest-runtime/src/__tests__/test_root/test_preprocessor.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/throwing-fn.js b/packages/jest-runtime/src/__tests__/test_root/throwing_fn.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/throwing-fn.js
rename to packages/jest-runtime/src/__tests__/test_root/throwing_fn.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/UTF8WithBOM.js b/packages/jest-runtime/src/__tests__/test_root/utf8_with_bom.js
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/UTF8WithBOM.js
rename to packages/jest-runtime/src/__tests__/test_root/utf8_with_bom.js
diff --git a/packages/jest-runtime/src/__tests__/test_root/UTF8WithBOM.json b/packages/jest-runtime/src/__tests__/test_root/utf8_with_bom.json
similarity index 100%
rename from packages/jest-runtime/src/__tests__/test_root/UTF8WithBOM.json
rename to packages/jest-runtime/src/__tests__/test_root/utf8_with_bom.json
diff --git a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/__mocks__/MyModule.js b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/__mocks__/my_module.js
similarity index 85%
rename from packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/__mocks__/MyModule.js
rename to packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/__mocks__/my_module.js
index c238d4b6775c..dece48e6245a 100644
--- a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/__mocks__/MyModule.js
+++ b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/__mocks__/my_module.js
@@ -8,4 +8,4 @@
 
 'use strict';
 
-exports.modulePath = 'subdir1/__mocks__/MyModule.js';
+exports.modulePath = 'subdir1/__mocks__/my_module.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/MyModule.js b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/my_module.js
similarity index 87%
rename from packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/MyModule.js
rename to packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/my_module.js
index ebffbf30be76..8a91474b48db 100644
--- a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/MyModule.js
+++ b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/my_module.js
@@ -8,4 +8,4 @@
 
 'use strict';
 
-exports.modulePath = 'subdir2/MyModule.js';
+exports.modulePath = 'subdir1/my_module.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/__mocks__/MyModule.js b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/__mocks__/MyModule.js
deleted file mode 100644
index b0b7a50d4a9e..000000000000
--- a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/__mocks__/MyModule.js
+++ /dev/null
@@ -1,11 +0,0 @@
-/**
- * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- */
-
-'use strict';
-
-exports.modulePath = 'subdir2/__mocks__/MyModule.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root/module_dir/moduleDirModule.js b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/__mocks__/my_module.js
similarity index 85%
rename from packages/jest-runtime/src/__tests__/test_root/module_dir/moduleDirModule.js
rename to packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/__mocks__/my_module.js
index c40f376bed09..1a644ae5fa04 100644
--- a/packages/jest-runtime/src/__tests__/test_root/module_dir/moduleDirModule.js
+++ b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/__mocks__/my_module.js
@@ -8,4 +8,4 @@
 
 'use strict';
 
-exports.modulePath = 'module_dir/moduleDirModule.js';
+exports.modulePath = 'subdir2/__mocks__/my_module.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/module_dir/moduleDirModule.js b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/module_dir/moduleDirModule.js
deleted file mode 100644
index b9f4e0a28d11..000000000000
--- a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/module_dir/moduleDirModule.js
+++ /dev/null
@@ -1,11 +0,0 @@
-/**
- * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- */
-
-'use strict';
-
-exports.modulePath = 'subdir2/module_dir/moduleDirModule.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/module_dir/module_dir_module.js b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/module_dir/module_dir_module.js
new file mode 100644
index 000000000000..145796b83885
--- /dev/null
+++ b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/module_dir/module_dir_module.js
@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+'use strict';
+
+exports.modulePath = 'subdir2/module_dir/module_dir_module.js';
diff --git a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/MyModule.js b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/my_module.js
similarity index 87%
rename from packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/MyModule.js
rename to packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/my_module.js
index a39d2eea1e9b..748327ed4b51 100644
--- a/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir1/MyModule.js
+++ b/packages/jest-runtime/src/__tests__/test_root_with_dup_mocks/subdir2/my_module.js
@@ -8,4 +8,4 @@
 
 'use strict';
 
-exports.modulePath = 'subdir1/MyModule.js';
+exports.modulePath = 'subdir2/my_module.js';
diff --git a/packages/jest-runtime/src/index.js b/packages/jest-runtime/src/index.js
index 99c04ceb5eeb..f27a4bf2a459 100644
--- a/packages/jest-runtime/src/index.js
+++ b/packages/jest-runtime/src/index.js
@@ -362,14 +362,14 @@ class Runtime {
       // If the actual module file has a __mocks__ dir sitting immediately next
       // to it, look to see if there is a manual mock for this file.
       //
-      // subDir1/MyModule.js
-      // subDir1/__mocks__/MyModule.js
-      // subDir2/MyModule.js
-      // subDir2/__mocks__/MyModule.js
+      // subDir1/my_module.js
+      // subDir1/__mocks__/my_module.js
+      // subDir2/my_module.js
+      // subDir2/__mocks__/my_module.js
       //
       // Where some other module does a relative require into each of the
       // respective subDir{1,2} directories and expects a manual mock
-      // corresponding to that particular MyModule.js file.
+      // corresponding to that particular my_module.js file.
       const moduleDir = path.dirname(modulePath);
       const moduleFileName = path.basename(modulePath);
       const potentialManualMock = path.join(
diff --git a/packages/jest-test-typescript-parser/src/__tests__/type_script_parser.test.js b/packages/jest-test-typescript-parser/src/__tests__/type_script_parser.test.js
index 1cfef59ce3fd..7999cd43e22b 100644
--- a/packages/jest-test-typescript-parser/src/__tests__/type_script_parser.test.js
+++ b/packages/jest-test-typescript-parser/src/__tests__/type_script_parser.test.js
@@ -9,6 +9,6 @@
 'use strict';
 
 const {parse} = require('../type_script_parser');
-const {parserTests} = require('../../../../fixtures/parserTests');
+const {parserTests} = require('../../../../fixtures/parser_tests');
 
 parserTests(parse);
diff --git a/packages/jest-validate/src/__tests__/fixtures/jest_config.js b/packages/jest-validate/src/__tests__/fixtures/jest_config.js
index 3c39fac6bf6c..96182af17529 100644
--- a/packages/jest-validate/src/__tests__/fixtures/jest_config.js
+++ b/packages/jest-validate/src/__tests__/fixtures/jest_config.js
@@ -101,7 +101,7 @@ const validConfig = {
   rootDir: '/',
   roots: ['<rootDir>'],
   setupFiles: ['<rootDir>/setup.js'],
-  setupTestFrameworkScriptFile: '<rootDir>/testSetupFile.js',
+  setupTestFrameworkScriptFile: '<rootDir>/test_setup_file.js',
   silent: true,
   snapshotSerializers: ['my-serializer-module'],
   testEnvironment: 'jest-environment-jsdom',
diff --git a/packages/pretty-format/src/__tests__/expect-util.js b/packages/pretty-format/src/__tests__/expect_util.js
similarity index 100%
rename from packages/pretty-format/src/__tests__/expect-util.js
rename to packages/pretty-format/src/__tests__/expect_util.js
diff --git a/packages/pretty-format/src/__tests__/html_element.test.js b/packages/pretty-format/src/__tests__/html_element.test.js
index 4cfabc627e2f..ba91c0ed66c8 100644
--- a/packages/pretty-format/src/__tests__/html_element.test.js
+++ b/packages/pretty-format/src/__tests__/html_element.test.js
@@ -12,7 +12,7 @@
 'use strict';
 
 const HTMLElementPlugin = require('../plugins/html_element');
-const toPrettyPrintTo = require('./expect-util').getPrettyPrint([
+const toPrettyPrintTo = require('./expect_util').getPrettyPrint([
   HTMLElementPlugin,
 ]);
 
diff --git a/packages/pretty-format/src/__tests__/immutable.test.js b/packages/pretty-format/src/__tests__/immutable.test.js
index 64b540627982..ffa432af477a 100644
--- a/packages/pretty-format/src/__tests__/immutable.test.js
+++ b/packages/pretty-format/src/__tests__/immutable.test.js
@@ -13,7 +13,7 @@ const Immutable = require('immutable');
 const ReactElementPlugin = require('../plugins/react_element');
 const ReactTestComponentPlugin = require('../plugins/react_test_component');
 const ImmutablePlugins = require('../plugins/immutable_plugins');
-const toPrettyPrintTo = require('./expect-util').getPrettyPrint(
+const toPrettyPrintTo = require('./expect_util').getPrettyPrint(
   [ReactElementPlugin, ReactTestComponentPlugin].concat(ImmutablePlugins),
 );
 
diff --git a/testSetupFile.js b/test_setup_file.js
similarity index 100%
rename from testSetupFile.js
rename to test_setup_file.js
diff --git a/yarn.lock b/yarn.lock
index c49f1f470ee6..a900c0e19e26 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2195,6 +2195,16 @@ eslint-plugin-react@^7.1.0:
     has "^1.0.1"
     jsx-ast-utils "^1.4.1"
 
+eslint-plugin-unicorn@^2.1.2:
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/eslint-plugin-unicorn/-/eslint-plugin-unicorn-2.1.2.tgz#99dffe9f4773b04bc39356a7febd64dd700274bc"
+  dependencies:
+    import-modules "^1.1.0"
+    lodash.camelcase "^4.1.1"
+    lodash.kebabcase "^4.0.1"
+    lodash.snakecase "^4.0.1"
+    lodash.upperfirst "^4.2.0"
+
 eslint-scope@^3.7.1:
   version "3.7.1"
   resolved "https://registry.yarnpkg.com/eslint-scope/-/eslint-scope-3.7.1.tgz#3d63c3edfda02e06e01a452ad88caacc7cdcb6e8"
@@ -2670,7 +2680,7 @@ glob-parent@^2.0.0:
   dependencies:
     is-glob "^2.0.0"
 
-glob@7.1.1, glob@^7.1.1:
+glob@7.1.1, glob@^7.1.0, glob@^7.1.1:
   version "7.1.1"
   resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.1.tgz#805211df04faaf1c63a3600306cdf5ade50b2ec8"
   dependencies:
@@ -2681,7 +2691,7 @@ glob@7.1.1, glob@^7.1.1:
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
-glob@^7.0.3, glob@^7.0.5, glob@^7.0.6, glob@^7.1.0, glob@^7.1.2:
+glob@^7.0.3, glob@^7.0.5, glob@^7.0.6, glob@^7.1.2:
   version "7.1.2"
   resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.2.tgz#c19c9df9a028702d678612384a6552404c636d15"
   dependencies:
@@ -2889,11 +2899,11 @@ https-browserify@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/https-browserify/-/https-browserify-1.0.0.tgz#ec06c10e0a34c0f2faf199f7fd7fc78fffd03c73"
 
-iconv-lite@0.4.13, iconv-lite@~0.4.13:
+iconv-lite@0.4.13:
   version "0.4.13"
   resolved "https://registry.yarnpkg.com/iconv-lite/-/iconv-lite-0.4.13.tgz#1f88aba4ab0b1508e8312acc39345f36e992e2f2"
 
-iconv-lite@0.4.15:
+iconv-lite@0.4.15, iconv-lite@~0.4.13:
   version "0.4.15"
   resolved "https://registry.yarnpkg.com/iconv-lite/-/iconv-lite-0.4.15.tgz#fe265a218ac6a57cfe854927e9d04c19825eddeb"
 
@@ -2913,6 +2923,10 @@ immutable@^4.0.0-rc.1:
   version "4.0.0-rc.2"
   resolved "https://registry.yarnpkg.com/immutable/-/immutable-4.0.0-rc.2.tgz#fdd0948aae728fda2306a02f72bb73e1773432d1"
 
+import-modules@^1.1.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/import-modules/-/import-modules-1.1.0.tgz#748db79c5cc42bb9701efab424f894e72600e9dc"
+
 imurmurhash@^0.1.4:
   version "0.1.4"
   resolved "https://registry.yarnpkg.com/imurmurhash/-/imurmurhash-0.1.4.tgz#9218b9b2b928a238b13dc4fb6b6d576f231453ea"
@@ -3716,6 +3730,10 @@ lodash.bind@^4.1.4:
   version "4.2.1"
   resolved "https://registry.yarnpkg.com/lodash.bind/-/lodash.bind-4.2.1.tgz#7ae3017e939622ac31b7d7d7dcb1b34db1690d35"
 
+lodash.camelcase@^4.1.1:
+  version "4.3.0"
+  resolved "https://registry.yarnpkg.com/lodash.camelcase/-/lodash.camelcase-4.3.0.tgz#b28aa6288a2b9fc651035c7711f65ab6190331a6"
+
 lodash.cond@^4.3.0:
   version "4.5.2"
   resolved "https://registry.yarnpkg.com/lodash.cond/-/lodash.cond-4.5.2.tgz#f471a1da486be60f6ab955d17115523dd1d255d5"
@@ -3752,6 +3770,10 @@ lodash.isarray@^3.0.0:
   version "3.0.4"
   resolved "https://registry.yarnpkg.com/lodash.isarray/-/lodash.isarray-3.0.4.tgz#79e4eb88c36a8122af86f844aa9bcd851b5fbb55"
 
+lodash.kebabcase@^4.0.1:
+  version "4.1.1"
+  resolved "https://registry.yarnpkg.com/lodash.kebabcase/-/lodash.kebabcase-4.1.1.tgz#8489b1cb0d29ff88195cceca448ff6d6cc295c36"
+
 lodash.keys@^3.0.0:
   version "3.1.2"
   resolved "https://registry.yarnpkg.com/lodash.keys/-/lodash.keys-3.1.2.tgz#4dbc0472b156be50a0b286855d1bd0b0c656098a"
@@ -3784,6 +3806,10 @@ lodash.reject@^4.4.0:
   version "4.6.0"
   resolved "https://registry.yarnpkg.com/lodash.reject/-/lodash.reject-4.6.0.tgz#80d6492dc1470864bbf583533b651f42a9f52415"
 
+lodash.snakecase@^4.0.1:
+  version "4.1.1"
+  resolved "https://registry.yarnpkg.com/lodash.snakecase/-/lodash.snakecase-4.1.1.tgz#39d714a35357147837aefd64b5dcbb16becd8f8d"
+
 lodash.some@^4.4.0:
   version "4.6.0"
   resolved "https://registry.yarnpkg.com/lodash.some/-/lodash.some-4.6.0.tgz#1bb9f314ef6b8baded13b549169b2a945eb68e4d"
@@ -3801,6 +3827,10 @@ lodash.templatesettings@^4.0.0:
   dependencies:
     lodash._reinterpolate "~3.0.0"
 
+lodash.upperfirst@^4.2.0:
+  version "4.3.1"
+  resolved "https://registry.yarnpkg.com/lodash.upperfirst/-/lodash.upperfirst-4.3.1.tgz#1365edf431480481ef0d1c68957a5ed99d49f7ce"
+
 lodash@^3.10.1, lodash@^3.8.0:
   version "3.10.1"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-3.10.1.tgz#5bf45e8e49ba4189e17d482789dfd15bd140b7b6"
@@ -5342,7 +5372,7 @@ subarg@^1.0.0:
   dependencies:
     minimist "^1.1.0"
 
-supports-color@3.1.2:
+supports-color@3.1.2, supports-color@^3.1.2:
   version "3.1.2"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-3.1.2.tgz#72a262894d9d408b956ca05ff37b2ed8a6e2a2d5"
   dependencies:
@@ -5352,12 +5382,6 @@ supports-color@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-2.0.0.tgz#535d045ce6b6363fa40117084629995e9df324c7"
 
-supports-color@^3.1.2:
-  version "3.2.3"
-  resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-3.2.3.tgz#65ac0504b3954171d8a64946b2ae3cbb8a5f54f6"
-  dependencies:
-    has-flag "^1.0.0"
-
 symbol-tree@^3.2.1:
   version "3.2.2"
   resolved "https://registry.yarnpkg.com/symbol-tree/-/symbol-tree-3.2.2.tgz#ae27db38f660a7ae2e1c3b7d1bc290819b8519e6"