Mocha & Chai

Installation

npm i -D mocha chai

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Usage

./node_modules/mocha/bin/mocha <test-file?> [option]

# Use with npm scripts
npm test -- [option]

// package.json e.g.:
{
  "scripts": {
    "test" : "mocha <test-file?> [option]"
  }
}

Options:

-b, --bail <boolean> (abort after first fail)
--exit <boolean> (force to quit after tests complete)
-j, --jobs <number> (jobs to run in parallel)
-p, --parallel <boolean>
--config <config-file> (.mocharc.js by default)
--extension [extension] (['js', 'cjs', 'mjs'] by default)
-w, --watch <boolean>
-r, --require <module> (preload modules before testing)

More at COMMAND-LINE USAGE (mochajs.org).

Configuration

// .mocharc.js e.g.:
'use-strict';

module.exports = {
  bail: true,
  extension: ['js'],
  // ...
}

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Using ESMs

1- Setup package file:

// package.json e.g.:
{
  "type": "module"
}

2- Setup test files:

// main.test.js e.g.:
import { assert } from 'chai';
import foo from './bar.js'; // *

*Use file extensions for relative/absolute module paths, see Mandatory file extensions (nodejs.org).

More at Assert (chaijs.com).

Using TypeScript ESMs

1- Install TypeScript, TS-Node for running .ts files like tsc + node, Mocha types, and Chai types:

npm i -D typescript ts-node @types/mocha @types/chai

2- Setup package file. To avoid conflicts with other tsconfig files, specify a different one through the environment variable TS_NODE_PROJECT (notice there’s no space after the path value):

// package.json e.g.:
{
  "type": "module",
  "scripts": {
    "test" : "set TS_NODE_PROJECT=tsconfig.test.json&& mocha"
    // Or "test" : "env TS_NODE_PROJECT=tsconfig.test.json mocha" on Linux/Mac?
  }
}

3- Setup Mocha configuration file:

// .mocharc.json e.g.:
{
  "experimental-json-modules": true,
  "extensions": [
    "ts"
  ],
  "loader": "ts-node/esm",
  "recursive": true,
  "spec": [
    "test/**/*.spec.ts"
  ]
}

4- Setup TypeScript configuration file (compilerOptions inside ts-node can override compilerOptions from outside it, which are the ones used by tsc):

// tsconfig.test.json e.g.:
{
  "ts-node": {
    "compilerOptions": {
      "allowSyntheticDefaultImports": true,
      "module": "ESNext",
      "moduleResolution": "node",
      "resolveJsonModule": true,
      "target": "ESNext"
    },
    "files": true,
    "esm": true
  }
}

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