brainstorm: `mocha-to-node-test-runner`

[AugustinMauroy]

Description

We need to brainstorm ideas for the mocha-to-node-test-runner codemod. It's will support converting Mocha v8 to node v22, v24.

Important points

• It's must not touch to the imports except mocha imports and node:test imports.
• It's should not convert the CB style from function() to arrow functions () => {} or vice versa.
• CJS/ESM should both be supported.

Examples

Example 1: Basic Test Case

Before:

const assert = require('assert');
describe('Array', function() {
  describe('#indexOf()', function() {
    it('should return -1 when the value is not present', function() {
      const arr = [1, 2, 3];
      assert.strictEqual(arr.indexOf(4), -1);
    });
  });
});

After:

const assert = require('assert');
const { describe, it } = require('node:test');
describe('Array', function() {
    describe('#indexOf()', () => {
        it('should return -1 when the value is not present', function() {
            const arr = [1, 2, 3];
            assert.strictEqual(arr.indexOf(4), -1);
        });
    });
});

Example 2: Async Test Case

Before:

const assert = require('assert');
describe('Async Test', function() {
    it('should complete after a delay', async function(done) {
        const result = await new Promise(resolve => setTimeout(() => resolve(42), 100));
        assert.strictEqual(result, 42);
    });
});

After:

const assert = require('assert');
const { describe, it } = require('node:test');
describe('Async Test', () => {
    it('should complete after a delay', async () => {
        const result = await new Promise(resolve => setTimeout(() => resolve(42), 100));
        assert.strictEqual(result, 42);
    });
});

Example 3: Hooks

Before:

const assert = require('assert');
const fs = require('fs');
describe('File System', function() {
    before(function() {
        fs.writeFileSync('test.txt', 'Hello, World!');
    });

    after(function() {
        fs.unlinkSync('test.txt');
    });

    it('should read the file', function() {
        const content = fs.readFileSync('test.txt', 'utf8');
        assert.strictEqual(content, 'Hello, World!');
    });
});

After:

const assert = require('assert');
const fs = require('fs');
const { describe, before, after, it } = require('node:test');
describe('File System', () => {
    before(() => {
        fs.writeFileSync('test.txt', 'Hello, World!');
    });

    after(() => {
        fs.unlinkSync('test.txt');
    });

    it('should read the file', () => {
        const content = fs.readFileSync('test.txt', 'utf8');
        assert.strictEqual(content, 'Hello, World!');
    });
});

Example 4: done Callback

Before:

const assert = require('assert');
describe('Callback Test', function() {
    it('should call done when complete', function(done) {
        setTimeout(() => {
            assert.strictEqual(1 + 1, 2);
            done();
        }, 100);
    });
});

After:

const assert = require('assert');
const { describe, it } = require('node:test');
describe('Callback Test', () => {
    it('should call done when complete', (t, done) => {
        setTimeout(() => {
            assert.strictEqual(1 + 1, 2);
            done();
        }, 100);
    });
});

Example 5: Skipped Tests

Before:

const assert = require('assert');
describe('Skipped Test', function() {
    it.skip('should not run this test', function() {
        assert.strictEqual(1 + 1, 3);
    });
    it('should also be skipped', function() {
        this.skip();
        assert.strictEqual(1 + 1, 3);
    });
});

After:

const assert = require('assert');
const { describe, it } = require('node:test');
describe('Skipped Test', () => {
    it.skip('should not run this test', () => {
        assert.strictEqual(1 + 1, 3);
    });
    it('should also be skipped', (t) => {
        assert.strictEqual(1 + 1, 3);
        t.skip();
    });
});

Example 6: Dynamic/generated tests

Before:

const assert = require('assert');
describe('Dynamic Tests', function() {
    const tests = [1, 2, 3];
    tests.forEach((test) => {
        it(`should handle test ${test}`, function() {
            assert.strictEqual(test % 2, 0);
        });
    });
});

After:

const assert = require('assert');
const { describe, it } = require('node:test');
describe('Dynamic Tests', () => {
    const tests = [1, 2, 3];
    tests.forEach((test) => {
        it(`should handle test ${test}`, () => {
            assert.strictEqual(test % 2, 0);
        });
    });
});

Example 7: Timeouts handling

This timeout handling work for describe, it and hooks.

Before:

const assert = require('assert');
describe('Timeout Test', function() {
    this.timeout(500);

    it('should complete within 100ms', function(done) {
        this.timeout(100);
        setTimeout(done, 500); // This will fail

    });

    it('should complete within 200ms', function() {
        this.timeout(200);
        setTimeout(done, 100); // This will pass
    });
});

After:

const assert = require('assert');
const { describe, it } = require('node:test');
describe('Timeout Test', { timeout: 500 }, () => {
    it('should complete within 100ms', { timeout: 100 }, (t, done) => {
        setTimeout(done, 500); // This will fail
    });

    it('should complete within 200ms', { timeout: 200 }, (t, done) => {
        setTimeout(done, 100); // This will pass
    });
});

Caveats

• node:test doesn't support the retry option that Mocha has, so any tests using that will need to be handled separately.

REFS

• Node Test Runner
• Mocha

[AugustinMauroy]

I don't know how do handle CLI part