add a basic mocha configuration (#85)

* add a basic mocha configuration

* Update validate.test.js

packages/eslint-config-twilio-mocha/.eslintrc

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+{
+  "extends": "twilio",
+  "parserOptions": {
+    "ecmaVersion": 9,
+    "sourceType": "module"
+  }
+}

packages/eslint-config-twilio-mocha/README.md

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+# eslint-config-twilio-mocha
+
+[![Version](https://img.shields.io/npm/v/eslint-config-twilio-mocha.svg?style=square)](https://www.npmjs.com/package/eslint-config-twilio-mocha)
+[![Downloads](https://img.shields.io/npm/dt/eslint-config-twilio-mocha.svg?style=square)](https://www.npmjs.com/package/eslint-config-twilio-mocha)
+[![License](https://img.shields.io/npm/l/eslint-config-twilio.svg?style=square)](../../LICENSE)
+
+Twilio's approach to Mocha/Chai styling.
+
+## Plugins and Extensions
+
+This config includes the following plugins and extensions:
+
+- [`eslint-plugin-chai-friendly`](https://www.npmjs.com/package/eslint-plugin-chai-friendly)
+
+## Installation
+
+```bash
+$ npm install eslint eslint-config-twilio-mocha --save-dev
+```
+
+## Usage
+
+Add the ESLint config to either your `package.json` or your `.eslintrc`:
+
+### package.json
+
+```json
+{
+  "name": "my-project",
+  "eslintConfig": {
+    "extends": [
+      "twilio-mocha"
+    ]
+  }
+}
+```
+
+### .eslintrc
+
+```json
+{
+  "extends": [
+    "twilio-mocha"
+  ]
+}
+```
+
+Then add the following two scripts for running and fixing your codebase:
+
+```json
+{
+  "scripts": {
+    "lint": "eslint --ext js --ext jsx src/ test/",
+    "lint:fix": "npm run lint -- --fix"
+  }
+}
+```
+
+### .prettier.js
+
+If you want to allow your IDE to auto-format your code as you save it, then create a `.prettierrc.js` and add:
+
+```js
+const baseConfig = require('./node_modules/eslint-config-twilio/rules/prettier');
+
+module.exports = {
+  ...baseConfig,
+};
+``` 

packages/eslint-config-twilio-mocha/index.js

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+const overrides = require('./overrides');
+
+module.exports = {
+  extends: ['twilio'],
+  plugins: ['chai-friendly'],
+  overrides: [overrides],
+};

packages/eslint-config-twilio-mocha/jest.config.js

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+const base = require('./../../jest.base');
+const pkg = require('./package');
+
+module.exports = {
+  ...base,
+  name: pkg.name,
+  displayName: pkg.name,
+  rootDir: '../..',
+  testMatch: [
+    `<rootDir>/packages/${pkg.name}/test/**/*.test.js`
+  ],
+};

packages/eslint-config-twilio-mocha/overrides/chai.js

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+module.exports = {
+  files: ['*.spec.js', '*.spec.jsx', '*.test.js', '*.test.jsx', '*.spec.ts', '*.spec.tsx', '*.test.ts', '*.test.tsx'],
+  rules: {
+    'no-unused-expressions': 'off',
+    'chai-friendly/no-unused-expressions': 'error',
+  },
+};

packages/eslint-config-twilio-mocha/overrides/index.js

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+/* eslint global-require: 0 */
+
+module.exports = {
+  ...require('./chai'),
+};