@wordpress/jest-console

@wordpress/jest-console

Custom Jest matchers for the Console object to test JavaScript code in WordPress.

This package converts console.error and console.warn functions into mocks and tracks their calls. It also enforces usage of one of the related matchers whenever tested code calls one of the mentioned console methods. It means that you need to assert with .toHaveErrored() or .toHaveErroredWith( arg1, arg2, ... ) when console.error gets executed, and .toHaveWarned() or .toHaveWarnedWith( arg1, arg2, ... ) when console.warn is called. Your test will fail otherwise! This is a conscious design decision which helps to detect deprecation warnings when upgrading dependent libraries or smaller errors when refactoring code.

Installation

Install the module:

npm install @wordpress/jest-console --save-dev

Setup

The simplest setup is to use Jest's setupTestFrameworkScriptFile config option:

"jest": {
  "setupTestFrameworkScriptFile": "./node_modules/@wordpress/jest-console/build/index.js"
},

If your project already has a script file which sets up the test framework, you will need the following import statement:

import '@wordpress/jest-console';

Usage

.toHaveErrored()

Use .toHaveErrored to ensure that console.error function was called.

For example, let's say you have a drinkAll( flavor ) function that makes you drink all available beverages. You might want to check if function calls console.error for 'octopus' instead, because 'octopus' flavor is really weird and why would anything be octopus-flavored? You can do that with this test suite:

describe( 'drinkAll', () => {
  test( 'drinks something lemon-flavored', () => {
    drinkAll( 'lemon' );
    expect( console ).not.toHaveErrored();
  } );

  test( 'errors when something is octopus-flavored', () => {
    drinkAll( 'octopus' );
    expect( console ).toHaveErrored();
  } );
} );

.toHaveErroredWith( arg1, arg2, ... )

Use .toHaveErroredWith to ensure that console.error function was called with specific arguments.

For example, let's say you have a drinkAll( flavor ) function again makes you drink all available beverages. You might want to check if function calls console.error with a specific message for 'octopus' instead, because 'octopus' flavor is really weird and why would anything be octopus-flavored? To make sure this works, you could write:

describe( 'drinkAll', () => {
  test( 'errors with message when something is octopus-flavored', () => {
    drinkAll( 'octopus' );
    expect( console ).toHaveErroredWith( 'Should I really drink something that is octopus-flavored?' );
  } );
} );

.toHaveWarned()

Use .toHaveWarned to ensure that console.warn function was called.

Almost identical usage as .toHaveErrored().

.toHaveWarnedWith( arg1, arg2, ... )

Use .toHaveWarneddWith to ensure that console.warn function was called with specific arguments.

Almost identical usage as .toHaveErroredWith().