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Mocha

Getting Started

1. Installation

First, install the mocha package as a devDependency using your favorite package manager:

Terminal window
npm i -D mocha

2. Test File

Create the following example.test.js file under a test/ directory:

test/example.test.js
import { assert } from "node:assert";


describe("Array", function () {
  describe("#indexOf()", function () {
    it("should return -1 when the value is not present", function () {
      assert.equal([1, 2, 3].indexOf(4), -1);
    });
  });
});

3. Running Mocha

Now, run npx mocha to execute the Mocha package on the newly created test file:

Terminal window
npx mocha

You should see passing output like:

  Array
    #indexOf()
      ✓ should return -1 when the value is not present


  1 passing (9ms)

Optional: test script

Most projects include a package.json "test" script:

package.json
{
  "scripts": {
    "test": "mocha"
  }
}

You can then run that script with your favorite package manager:

Terminal window
npm run test

Next Steps

See:

  • CLI for the commands you can pass to mocha
  • Configuring for creating a persistent test configuration file
  • Editor Plugins for improving the Mocha experience in your editor

You can see real live live example code in our example repositories: