jest-mock-console

Jest utility to mock the console

Table of Contents

• Problem
• Solution
• Installation
• Basic Example
• Advanced Example
• Analyze all logs
• mockConsole(mocks)
  • default
  • string
  • array
  • object

The problem

If you use console or prop-types in your app, and you use jest then you end up with tests that look like:

This is not helpful as all of the tests have passed, but you are seeing red. It is especially unhelpful when there is an actual failure as you have to search through all the red to find the actual failed test.

The solution

This allows you to mock and unmock the console at will, so your tests look like:

This is much more helpful as you don't see red on success anymore. Then you know when you see red text you know something went wrong.

Installation

This module is distributed view npm which is bundled with node and should be installed as one of your project's devDependencies:

npm install --save-dev jest-mock-console

Basic Example

At the top of your test file:

import mockConsole from "jest-mock-console";

Then your tests

describe(...
  it(...
    const restoreConsole = mockConsole();  // mockConsole returns a function to restore it back to normal
    console.error('This will not show in the test report');
    expect(console.error).toHaveBeenCalled();
    restoreConsole();
  )
)

However you always need to restore the console after each test or you will break jest. This is where the setupTestFramework file comes in.

Advanced Example

If you don't want to worry about accidentally forgetting to restoreConsole() after your tests you can modify jest to unmock after every it(...).

In your jest config:

setupFilesAfterEnv: ["jest-mock-console/dist/setupTestFramework.js"];

Then in your test files:

import mockConsole from 'jest-mock-console';

describe(...
  it(...
    mockConsole();
    console.error('This will not show in the test report');
    expect(console.error).toHaveBeenCalled();
    // No need for restoreConsole as it is called after every `it(...)`
  )
)

Analyze all logs

In some circumstances Jest is infamous for logging because it overwrites the bash output. If you're experiencing this kind of logging frustration and you need to analyze all the console.log call arguments (typically to understand why a test is failing) you can temporarily add an expect statement on the console itself.

In your test files:

describe(...
  it(...
    const restoreConsole = mockConsole();
    console.error('This will not show in the test report');
    expect(console.error.mock.calls).toEqual([]);
    restoreConsole();
  )
)

the test looks like:

mockConsole(mocks)

• mocks[string,array,object]: The properties of the console you want to mock. Defaults to ['log','warn','error']
  • default - Will mock console.log, console.warn, and console.error

    mockConsole() // same as `mockConsole(['log','warn','error'])
    

  • string - You can mock a single function

    mockConsole('error')
    

  • array - You can mock multiple functions

    mockConsole(['log', 'info'])
    

  • object - You can set custom functions for console

    const originalConsole = window.console;
    mockConsole({
      error: (...args) => originalConsole.log(`console.error of: ${...args}`)
    })
    

LICENSE

MIT