"TypeError: matcherResult.message is not a function"

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:

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

This will throw the following error in Jest:

1Expect takes at most one argument.

Solution

jest-27-expect-message allows you to call expect with a second argument of a String message.

For example the same test as above:

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

With jest-27-expect-message this will fail with your custom error message:

1  ● returns 2 when adding 1 and 1
2
3    Custom message:
4      Woah this should be 2!
5
6    expect(received).toBe(expected) // Object.is equality
7
8    Expected: 3
9    Received: 2

Installation

With npm:

1npm install --save-dev jest-27-expect-message

With yarn:

1yarn add -D jest-27-expect-message

Setup

Add jest-27-expect-message to your Jest setupFilesAfterEnv configuration. See for help

Jest v24+

1"jest": {
2  "setupFilesAfterEnv": ["jest-27-expect-message"]
3}

Jest v23-

1"jest": {
2  "setupTestFrameworkScriptFile": "jest-27-expect-message"
3}

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.

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

Contributors

Matt Phillips 💻 📖 💡 🤔 🚇 ⚠️ 🔧

LICENSE

MIT