Egg provides a dedicated mocking helper package for application unit tests: @eggjs/mock (historically known as egg-mock).

• Repository (Egg 3.x / egg-mock@5.x, peerDependencies.egg: ^3.12.0): https://github.com/eggjs/mock/tree/5.x
• API reference: see README in the repo.

@eggjs/mock is built on top of mm (Mock Mate), which provides low-level monkey-patching utilities.

• Repository: https://github.com/node-modules/mm

Install

npm i @eggjs/mock --save-dev

In many docs / legacy code you may still see egg-mock. For Egg 3.x, the recommended package name is @eggjs/mock.

Quick Start

Create an app instance

const mock = require('@eggjs/mock');

describe('test/controller/home.test.js', () => {
  let app;

  before(async () => {
    app = mock.app({ baseDir: 'path/to/your/app' });
    await app.ready();
  });

  after(() => app.close());
});

Use bootstrap to avoid repeated setup

const { app, mock, assert } = require('egg-mock/bootstrap');

describe('test/controller/home.test.js', () => {
  // test cases
});

The bootstrap helper wires common setup/teardown and is convenient for most projects.

Create a Context

it('should get a ctx', () => {
  const ctx = app.mockContext();
  assert(ctx.method === 'GET');
});

it('should mock ctx.user', () => {
  const ctx = app.mockContext({
    user: { name: 'fengmk2' },
  });
  assert(ctx.user.name === 'fengmk2');
});

Restore after each test

When using mm / @eggjs/mock, remember to restore mocked state:

const mm = require('mm');

afterEach(() => mm.restore());

If you use egg-mock/bootstrap, it already restores mocks for you in afterEach.

mm (Mock Mate) API

mm is a general purpose monkey-patching library. @eggjs/mock is built on top of it, and many Egg tests use mm directly.

Prefer using @eggjs/mock exports

For consistency inside the Egg ecosystem, prefer the mm that is exported by @eggjs/mock (egg-mock). It is compatible with mm and adds Egg-specific helpers.

// CJS
const { app, mm } = require('egg-mock/bootstrap');
// mm.restore() in afterEach is already wired by bootstrap

// or
const mock = require('@eggjs/mock');
mock(target, 'prop', value);
mock.restore();

You can still use the standalone mm package directly if needed:

import mm, { restore } from 'mm';

Core

• mm(target, property, value) / mm.mock(...): monkey-patch a property.
• mm.restore() / restore(): restore all patched properties.
• mm.isMocked(target, property): check if a property is mocked.
• mm.spy(target, method): spy a function (records call counts/args).

When a mocked property is a function, mm will attach spy fields like called, calledArguments, lastCalledArguments.

Callback-style helpers

• mm.data(target, method, data[, timeout]): callback returns (null, data).
• mm.datas(target, method, datas[, timeout]): callback returns (null, ...datas).
• mm.empty(target, method[, timeout]): callback returns (null, null).
• mm.error(target, method, error[, props|timeout][, timeout]): callback returns an error.
• mm.errorOnce(...): like error but only once.

Sync helpers

• mm.syncData(target, method, value): return value.
• mm.syncEmpty(target, method): return undefined.
• mm.syncError(target, method, error[, props]): throw error.

HTTP helpers

• mm.http.request(url, data[, headers][, delay]): mock http.request / http.get.
• mm.http.requestError(url[, reqError][, resError][, delay]): mock request/response errors.
• mm.https.request(...) / mm.https.requestError(...): same for https.

Other

• mm.spawn(code, stdout, stderr[, timeout]): mock child_process.spawn.
• mm.classMethod(instance, method, mockFn): mock a class method via prototype.

For complete and up-to-date details, see the mm repository: https://github.com/node-modules/mm