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:

``js
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:

`sh
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:

`js
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:

`sh
● 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:

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

With yarn:

`sh
yarn add -D jest-expect-message
`

Setup

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

$3

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

$3

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

If you have a custom setup file and want to use this library then add the following to your setup file.

`js
import 'jest-expect-message';
`

$3

Add the following entry to your tsconfig to enable Typescript support.

`json
"files": ["node_modules/jest-expect-message/types/index.d.ts"],
`

#### Example

Custom message example with typescript

$3

`json
"rules": {
"jest/valid-expect": [
"error",
{
"maxArgs": 2
}
]
}
`

Usage

- expect(actual, message, options?)
- 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.
- options: An optional object that controls what is shown as part of the custom message.
- showPrefix: boolean: If false will not show the Custom message: prefix. Default: true
- showMatcherMessage: boolean: If false will not show the matchers original error message. Default: true
- showStack: boolean: If false will not show the matchers stack trace. Default: true

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

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

$3

`js
test('returns 2 when adding 1 and 1', () => {
expect(1 + 1, 'Woah this should be 2!', { showPrefix: false }).toBe(3);
});
// ↓ ↓ ↓ ↓ ↓ ↓
/*
● returns 2 when adding 1 and 1

Woah this should be 2!

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

Expected: 3
Received: 2

1 | test('returns 2 when adding 1 and 1', () => {
> 2 | expect(1 + 1, 'Woah this should be 2!', { showPrefix: false }).toBe(3);
| ^
3 | });
*/
`

$3

`js
test('returns 2 when adding 1 and 1', () => {
expect(1 + 1, 'Woah this should be 2!', { showMatcherMessage: false }).toBe(3);
});
// ↓ ↓ ↓ ↓ ↓ ↓
/*
● returns 2 when adding 1 and 1

Custom message:
Woah this should be 2!

1 | test('returns 2 when adding 1 and 1', () => {
> 2 | expect(1 + 1, 'Woah this should be 2!', { showMatcherMessage: false }).toBe(3);
| ^
3 | });
*/
`

$3

`js
test('returns 2 when adding 1 and 1', () => {
expect(1 + 1, 'Woah this should be 2!', { showStack: false }).toBe(3);
});
// ↓ ↓ ↓ ↓ ↓ ↓
/*
● 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
*/
``

LICENSE

MIT