テストでのモック

import foo from './foo.mjs';

export function main() {
  const f = foo();
}

import bar from 'bar';

export function main() {
  const f = bar();
}

import assert from 'node:assert/strict';
import { before, describe, it, mock } from 'node:test';

describe('foo', { concurrency: true }, () => {
  const barMock = mock.fn();
  let foo;

  before(async () => {
    const barNamedExports = await import('./bar.mjs')
      // discard the original default export
      .then(({ default: _, ...rest }) => rest);

    // It's usually not necessary to manually call restore() after each
    // nor reset() after all (node does this automatically).
    mock.module('./bar.mjs', {
      defaultExport: barMock,
      // Keep the other exports that you don't want to mock.
      namedExports: barNamedExports,
    });

    // This MUST be a dynamic import because that is the only way to ensure the
    // import starts after the mock has been set up.
    ({ foo } = await import('./foo.mjs'));
  });

  it('should do the thing', () => {
    barMock.mock.mockImplementationOnce(function bar_mock() {
      /* … */
    });

    assert.equal(foo(), 42);
  });
});

import assert from 'node:assert/strict';
import { beforeEach, describe, it } from 'node:test';

import { MockAgent, setGlobalDispatcher } from 'undici';

import endpoints from './endpoints.mjs';

describe('endpoints', { concurrency: true }, () => {
  let agent;
  beforeEach(() => {
    agent = new MockAgent();
    setGlobalDispatcher(agent);
  });

  it('should retrieve data', async () => {
    const endpoint = 'foo';
    const code = 200;
    const data = {
      key: 'good',
      val: 'item',
    };

    agent
      .get('https://example.com')
      .intercept({
        path: endpoint,
        method: 'GET',
      })
      .reply(code, data);

    assert.deepEqual(await endpoints.get(endpoint), {
      code,
      data,
    });
  });

  it('should save data', async () => {
    const endpoint = 'foo/1';
    const code = 201;
    const data = {
      key: 'good',
      val: 'item',
    };

    agent
      .get('https://example.com')
      .intercept({
        path: endpoint,
        method: 'PUT',
      })
      .reply(code, data);

    assert.deepEqual(await endpoints.save(endpoint), {
      code,
      data,
    });
  });
});

import assert from 'node:assert/strict';
import { describe, it, mock } from 'node:test';

import ago from './ago.mjs';

describe('whatever', { concurrency: true }, () => {
  it('should choose "minutes" when that\'s the closet unit', () => {
    mock.timers.enable({ now: new Date('2000-01-01T00:02:02Z') });

    const t = ago('1999-12-01T23:59:59Z');

    assert.equal(t, '2 minutes ago');
  });
});