---

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 setupFilesAfterEnv configuration. See for help

Jest v24+

Add this to package.json

"jest": {
  "setupFilesAfterEnv": ["jest-expect-message"]
}

Or if you encountered with this error "We detected setupFilesAfterEnv in your package.json ...", undo setupFilesAfterEnv and create a file src/setupTests.js containing a requirement statement:

// src/setupTests.js
require("jest-expect-message")

Jest v23-

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

Usage

• expect(actual, message, wrapper)
  • 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.
  • wrapper (optional): Function, if you want to wrap the message with a custom text instead of default "Custom message:...".

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

// with a custom wrapper
test('returns 2 when adding 1 and 1', () => {
  const wrapper = msg => `| Custom Message << ${msg} >> |`
  expect(1 + 1, 'Woah this should be 2!', wrapper).toBe(3);
});

Contributors

Matt Phillips 💻 📖 💡 🤔 🚇 ⚠️ 🔧	Mohammad 💻 📖 💡 🤔 ⚠️

LICENSE

MIT