This function is used to mock the exports of ECMAScript modules, CommonJS modules, JSON modules, and Node.js builtin modules. Any references to the original module prior to mocking are not impacted. In order to enable module mocking, Node.js must be started with the --experimental-test-module-mocks command-line flag.
The following example demonstrates how a mock is created for a module.
test('mocks a builtin module in both module systems', async (t) => {
// Create a mock of 'node:readline' with a named export named 'fn', which
// does not exist in the original 'node:readline' module.
const mock = t.mock.module('node:readline', {
namedExports: { fn() { return 42; } },
});
let esmImpl = await import('node:readline');
let cjsImpl = require('node:readline');
// cursorTo() is an export of the original 'node:readline' module.
assert.strictEqual(esmImpl.cursorTo, undefined);
assert.strictEqual(cjsImpl.cursorTo, undefined);
assert.strictEqual(esmImpl.fn(), 42);
assert.strictEqual(cjsImpl.fn(), 42);
mock.restore();
// The mock is restored, so the original builtin module is returned.
esmImpl = await import('node:readline');
cjsImpl = require('node:readline');
assert.strictEqual(typeof esmImpl.cursorTo, 'function');
assert.strictEqual(typeof cjsImpl.cursorTo, 'function');
assert.strictEqual(esmImpl.fn, undefined);
assert.strictEqual(cjsImpl.fn, undefined);
});