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test_runner: support module mocking · nodejs/node@7a67ecf · GitHub

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test_runner: support module mocking
This commit adds experimental module mocking to the test runner. PR-URL: #52848 Fixes: #51164 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Moshe Atlow <moshe@atlow.co.il> Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com> Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
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‎doc/api/cli.md‎

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@@ -979,6 +979,16 @@ generated as part of the test runner output. If no tests are run, a coverage
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report is not generated. See the documentation on
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[collecting code coverage from tests][] for more details.
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### `--experimental-test-module-mocks`
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<!-- YAML
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added: REPLACEME
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-->
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> Stability: 1.0 - Early development
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Enable module mocking in the test runner.
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### `--experimental-vm-modules`
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<!-- YAML

‎doc/api/test.md‎

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Resets the implementation of the mock function to its original behavior. The
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mock can still be used after calling this function.
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## Class: `MockModuleContext`
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<!-- YAML
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added: REPLACEME
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-->
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> Stability: 1.0 - Early development
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The `MockModuleContext` class is used to manipulate the behavior of module mocks
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created via the [`MockTracker`][] APIs.
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### `ctx.restore()`
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<!-- YAML
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added: REPLACEME
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-->
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Resets the implementation of the mock module.
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## Class: `MockTracker`
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<!-- YAML
@@ -1900,6 +1919,68 @@ test('spies on an object method', (t) => {
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});
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```
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### `mock.module(specifier[, options])`
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<!-- YAML
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added: REPLACEME
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-->
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> Stability: 1.0 - Early development
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* `specifier` {string} A string identifying the module to mock.
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* `options` {Object} Optional configuration options for the mock module. The
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following properties are supported:
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* `cache` {boolean} If `false`, each call to `require()` or `import()`
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generates a new mock module. If `true`, subsequent calls will return the same
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module mock, and the mock module is inserted into the CommonJS cache.
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**Default:** false.
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* `defaultExport` {any} An optional value used as the mocked module's default
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export. If this value is not provided, ESM mocks do not include a default
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export. If the mock is a CommonJS or builtin module, this setting is used as
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the value of `module.exports`. If this value is not provided, CJS and builtin
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mocks use an empty object as the value of `module.exports`.
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* `namedExports` {Object} An optional object whose keys and values are used to
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create the named exports of the mock module. If the mock is a CommonJS or
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builtin module, these values are copied onto `module.exports`. Therefore, if a
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mock is created with both named exports and a non-object default export, the
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mock will throw an exception when used as a CJS or builtin module.
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* Returns: {MockModuleContext} An object that can be used to manipulate the mock.
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This function is used to mock the exports of ECMAScript modules, CommonJS
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modules, and Node.js builtin modules. Any references to the original module
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prior to mocking are not impacted. The following example demonstrates how a mock
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is created for a module.
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```js
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test('mocks a builtin module in both module systems', async (t) => {
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// Create a mock of 'node:readline' with a named export named 'fn', which
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// does not exist in the original 'node:readline' module.
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const mock = t.mock.module('node:readline', {
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namedExports: { fn() { return 42; } },
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});
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let esmImpl = await import('node:readline');
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let cjsImpl = require('node:readline');
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// cursorTo() is an export of the original 'node:readline' module.
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assert.strictEqual(esmImpl.cursorTo, undefined);
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assert.strictEqual(cjsImpl.cursorTo, undefined);
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assert.strictEqual(esmImpl.fn(), 42);
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assert.strictEqual(cjsImpl.fn(), 42);
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mock.restore();
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// The mock is restored, so the original builtin module is returned.
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esmImpl = await import('node:readline');
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cjsImpl = require('node:readline');
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assert.strictEqual(typeof esmImpl.cursorTo, 'function');
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assert.strictEqual(typeof cjsImpl.cursorTo, 'function');
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assert.strictEqual(esmImpl.fn, undefined);
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assert.strictEqual(cjsImpl.fn, undefined);
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});
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```
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### `mock.reset()`
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<!-- YAML

‎doc/node.1‎

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.It Fl -experimental-test-coverage
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Enable code coverage in the test runner.
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.
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.It Fl -experimental-test-module-mocks
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Enable module mocking in the test runner.
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.
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.It Fl -experimental-eventsource
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Enable experimental support for the EventSource Web API.
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.

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