mockable-modules

A non-transpiling, non-configuration intense way to mock ES Modules for your tests. Built specifically to work nicely with the native Node.js test runner.

Install

npm install mockable-modules

Usage

Some code to test:

import { unpredictableFunction } from "db";

export const unpredictable = mockable(unpredictableFunction);

export async function action() {
	const result = unpredictable();

	return result;
}

And a test:

import { assert } from "mockable-modules/assert";
import { action, unpredictable } from "./index.js";

test("synchronous passing test", (t) => {
	const mock = unpredictable.tOverride(t, () => {
		return 12;
	});

	assert.calledOnce(mock);
});

Core API

mockable(fn)

Wraps a function's implementation to make it mockable

Example:

const mockableThing = mockable(thing);

disableMockable()

Disables the library in the given environment. You'll want to call this as early as possible in your production environment.

Example:

disableMockable();

.override(t, fn)

Override a mockable within test context t. Returns fn wrapped as a mock.fn. Clears the mock automatically when the test context ends.

Example:

import { whatever } from "./target.js";

test("a test", (t) => {
  const mockFn = whatever.override(t, () => "yes");

  // do some things

  // assert some things
});

Assertions

All of the assertions provided by this package are for asserting against Node's mock.fn instances.

Mockable Modules includes two ways for importing assertions.

• import assert from "mockable-modules" - Wraps node:assert/strict to include the assertions from Mockable Modules.
• import * as assertions from "mockable-modules/assertions" - Import just the Mockable Modules assertions.

assert.notCalled(mockFn)

Assert that mockFn has not been called.

Example:

test("a test", (t) => {
  const mockFn = whatever.override(t, () => "yes");

  // do some things

  assert.notCalled(mockFn);
});

assert.calledOnce(mockFn)

Assert that mockFn has been called exactly once.

Example:

test("a test", (t) => {
  const mockFn = whatever.override(t, () => "yes");

  // do some things

  assert.calledOnce(mockFn);
});

assert.calledOnce(mockFn)

Assert that mockFn has been called exactly once.

Example:

test("a test", (t) => {
  const mockFn = whatever.override(t, () => "yes");

  // do some things

  assert.calledOnce(mockFn);
});

assert.calledOnce(mockFn)

Assert that mockFn has been called exactly once.

Example:

test("a test", (t) => {
  const mockFn = whatever.override(t, () => "yes");

  // do some things

  assert.calledOnce(mockFn);
});

assert.calledTimes(mockFn, count)

Assert that mockFn has been called exactly count times.

Example:

test("a test", (t) => {
  const mockFn = whatever.override(t, () => "yes");

  // do some things

  assert.calledTimes(mockFn, 3);
});

assert.calledWith(mockFn, ...args)

Assert that mockFn has been called at least once with the given args

Example:

test("a test", (t) => {
  const mockFn = whatever.override(t, (x, y) => x + y);

  // do some things

  assert.calledWith(mockFn, 5, 3);
});

License

This code is licensed under the MIT license. See LICENSE for more information.