jest-expect-message
Add custom message to Jest expects
Last updated 2 years ago by mattphillips .
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jest-expect-message

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Add custom message to Jest expects


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Problem

In many testing libraries it is possible to supply a custom message for a given expectation, this is currently not possible in Jest.

For example:

test('returns 2 when adding 1 and 1', () => {
  expect(1 + 1, 'Woah this should be 2!').toBe(3);
});

This will throw the following error in Jest:

Expect takes at most one argument.

Solution

jest-expect-message allows you to call expect with a second argument of a String message.

For example the same test as above:

test('returns 2 when adding 1 and 1', () => {
  expect(1 + 1, 'Woah this should be 2!').toBe(3);
});

With jest-expect-message this will fail with your custom error message:

  ● returns 2 when adding 1 and 1

    Custom message:
      Woah this should be 2!

    expect(received).toBe(expected) // Object.is equality

    Expected: 3
    Received: 2

Installation

With npm:

npm install --save-dev jest-expect-message

With yarn:

yarn add -D jest-expect-message

Setup

Add jest-expect-message to your Jest setupTestFrameworkScriptFile configuration. See for help

"jest": {
  "setupTestFrameworkScriptFile": "jest-expect-message"
}

Usage

  • expect(actual, message)
    • actual: The value you would normally pass into an expect to assert against with a given matcher.
    • message: String, the custom message you want to be printed should the expect fail.
test('returns 2 when adding 1 and 1', () => {
  expect(1 + 1, 'Woah this should be 2!').toBe(3);
});

Contributors


Matt Phillips

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LICENSE

MIT

Current Tags

  • 1.0.2                                ...           latest (2 years ago)

3 Versions

  • 1.0.2                                ...           2 years ago
  • 1.0.1                                ...           2 years ago
  • 1.0.0                                ...           2 years ago

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