feat: add lowercase-description rule (#56)

Fixes #46

README.md

@@ -81,6 +81,7 @@ for more information about extending configuration files.
 | Rule                                                               | Description                                                       | Recommended                                                             | Fixable                                                     |
 | ------------------------------------------------------------------ | ----------------------------------------------------------------- | ----------------------------------------------------------------------- | ----------------------------------------------------------- |
 | [consistent-test-it](docs/rules/consistent-test-it.md)             | Enforce consistent test or it keyword                             |                                                                         | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
+| [lowercase-name](docs/rules/lowercase-name.md)                     | Disallow capitalized test names                                   |                                                                         |                                                             |
 | [no-disabled-tests](docs/rules/no-disabled-tests.md)               | Disallow disabled tests                                           | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
 | [no-focused-tests](docs/rules/no-focused-tests.md)                 | Disallow focused tests                                            | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
 | [no-hooks](docs/rules/no-hooks.md)                                 | Disallow setup and teardown hooks                                 |                                                                         |                                                             |

docs/rules/lowercase-name.md

@@ -0,0 +1,23 @@
+# Enforce lowercase test names (lowercase-name)
+
+## Rule details
+
+Enforce `it`, `test` and `describe` to have descriptions that begin with a
+lowercase letter. This provides more readable test failures. This rule is not
+enabled by default.
+
+The following pattern is considered a warning:
+
+```js
+it('Adds 1 + 2 to equal 3', () => {
+  expect(sum(1, 2)).toBe(3);
+});
+```
+
+The following pattern is not considered a warning:
+
+```js
+it('adds 1 + 2 to equal 3', () => {
+  expect(sum(1, 2)).toBe(3);
+});
+```

index.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const consistentTestIt = require('./rules/consistent-test-it');
+const lowercaseName = require('./rules/lowercase-name');
 const noDisabledTests = require('./rules/no-disabled-tests');
 const noFocusedTests = require('./rules/no-focused-tests');
 const noHooks = require('./rules/no-hooks');
@@ -61,6 +62,7 @@ module.exports = {
   },
   rules: {
     'consistent-test-it': consistentTestIt,
+    'lowercase-name': lowercaseName,
     'no-disabled-tests': noDisabledTests,
     'no-focused-tests': noFocusedTests,
     'no-hooks': noHooks,

rules/__tests__/lowercase-name.test.js

@@ -0,0 +1,130 @@
+'use strict';
+
+const RuleTester = require('eslint').RuleTester;
+const rules = require('../..').rules;
+
+const ruleTester = new RuleTester({
+  parserOptions: {
+    ecmaVersion: 6,
+  },
+});
+
+ruleTester.run('lowercase-name', rules['lowercase-name'], {
+  valid: [
+    "it(' ', function () {})",
+    'it(" ", function () {})',
+    'it(` `, function () {})',
+    "it('foo', function () {})",
+    'it("foo", function () {})',
+    'it(`foo`, function () {})',
+    'it("<Foo/>", function () {})',
+    'it("123 foo", function () {})',
+    'it(42, function () {})',
+    "test('foo', function () {})",
+    'test("foo", function () {})',
+    'test(`foo`, function () {})',
+    'test("<Foo/>", function () {})',
+    'test("123 foo", function () {})',
+    'test("42", function () {})',
+    "describe('foo', function () {})",
+    'describe("foo", function () {})',
+    'describe(`foo`, function () {})',
+    'describe("<Foo/>", function () {})',
+    'describe("123 foo", function () {})',
+    'describe("42", function () {})',
+    'describe(function () {})',
+  ],
+
+  invalid: [
+    {
+      code: "it('Foo', function () {})",
+      errors: [
+        {
+          message: '`it`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: 'it("Foo", function () {})',
+      errors: [
+        {
+          message: '`it`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: 'it(`Foo`, function () {})',
+      errors: [
+        {
+          message: '`it`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: "test('Foo', function () {})",
+      errors: [
+        {
+          message: '`test`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: 'test("Foo", function () {})',
+      errors: [
+        {
+          message: '`test`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: 'test(`Foo`, function () {})',
+      errors: [
+        {
+          message: '`test`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: "describe('Foo', function () {})",
+      errors: [
+        {
+          message: '`describe`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: 'describe("Foo", function () {})',
+      errors: [
+        {
+          message: '`describe`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+    {
+      code: 'describe(`Foo`, function () {})',
+      errors: [
+        {
+          message: '`describe`s should begin with lowercase',
+          column: 1,
+          line: 1,
+        },
+      ],
+    },
+  ],
+});

rules/lowercase-name.js

@@ -0,0 +1,70 @@
+'use strict';
+
+const isItTestOrDescribeFunction = node => {
+  return (
+    node.type === 'CallExpression' &&
+    node.callee &&
+    (node.callee.name === 'it' ||
+      node.callee.name === 'test' ||
+      node.callee.name === 'describe')
+  );
+};
+
+const isItDescription = node => {
+  return (
+    node.arguments &&
+    node.arguments[0] &&
+    (node.arguments[0].type === 'Literal' ||
+      node.arguments[0].type === 'TemplateLiteral')
+  );
+};
+
+const testDescription = node => {
+  const firstArgument = node.arguments[0];
+  const type = firstArgument.type;
+
+  if (type === 'Literal') {
+    return firstArgument.value;
+  }
+
+  // `isItDescription` guarantees this is `type === 'TemplateLiteral'`
+  return firstArgument.quasis[0].value.raw;
+};
+
+const descriptionBeginsWithLowerCase = node => {
+  if (isItTestOrDescribeFunction(node) && isItDescription(node)) {
+    const description = testDescription(node);
+    if (!description[0]) {
+      return false;
+    }
+
+    if (description[0] !== description[0].toLowerCase()) {
+      return node.callee.name;
+    }
+  }
+  return false;
+};
+
+module.exports = {
+  meta: {
+    docs: {
+      url:
+        'https://github.com/jest-community/eslint-plugin-jest/blob/master/docs/rules/lowercase-name.md',
+    },
+  },
+  create(context) {
+    return {
+      CallExpression(node) {
+        const erroneousMethod = descriptionBeginsWithLowerCase(node);
+
+        if (erroneousMethod) {
+          context.report({
+            message: '`{{ method }}`s should begin with lowercase',
+            data: { method: erroneousMethod },
+            node: node,
+          });
+        }
+      },
+    };
+  },
+};