Jest Mock Module

Extends jest to allow deep auto mocking of a module by spying on all functions and properties.

Introduction

Getting Started

Install the extension using pnpm, npm, yarn etc.

npm install -D "jest-mock-module"

The Jest Object

The jest object needs to be extended in every test file. This allows access to the jest-mock-module api.

jest.spy(moduleName)

This works like jest.doMock.

The main difference is a factory does not need to be provided as it automatically generates one using jest.createSpyFromModule.

Internally uses jest.mock so works with other jest mocking methods.

jest.createSpyFromModule(moduleName)

This works like jest.createMockFromModule.

The main difference is the returned mock is created using jest.spyOnObject.

jest.spyOnObject(object)

This creates a deep mock of the object spying on all the internal properties using jest-spy-on.

Example Usage

// src/example.js
module.exports = {
  testing: "123";
  nested: {
    test: () => true;
    testing: "456";
  }
}

import * as mock from "jest-mock-module";
mock.extend(jest);

// Only to be used on valid modules
jest.spy("src/example");

// Since babel-jest does not hoist jest.spy
// import calls need to come after the spy mock
const example = require("src/example");

// Check module object properties
jest.isMockProp(example, "testing"); // true
console.log(example.testing); // 123

// Respy on module object to get mockable
jest.spyOn(example).testing.mockValueOnce("789");
console.log(example.testing); // 789
console.log(example.testing); // 123

// Check module nested object properties
jest.isMockMethod(example.nested.test); // true
jest.isMockProp(example.nested, "testing"); // true

It keeps the same structure of the module but replaces all functions and properties with jest mocks.

• jest.createSpyFromModule is exported and can be used like jest.createMockFromModule. It is used internally by jest.spy in combination with jest.mock to provide a factory in place of Jest's automocking feature.

References

• jest-spy-on - Guide to spying on module methods
• jest-mock-props - Guide to spying on object properties