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Docs: Add assert.rejects API documentation.
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--- | ||
layout: default | ||
title: rejects | ||
description: Test if the provided promise rejects, and optionally compare the rejection value. | ||
categories: | ||
- assert | ||
--- | ||
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## `rejects( promise, expected [, message ] )` | ||
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Test if the provided promise rejects, and optionally compare the rejection value. | ||
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| name | description | | ||
|--------------------|--------------------------------------| | ||
| `promise` (thenable) | promise to test for rejection | | ||
| `expected` | Expected rejection value (generally an error) | | ||
| `message` (string) | A short description of the assertion | | ||
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### Description | ||
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When testing code that is expected to return a rejected promise based on a | ||
specific set of circumstances, use `assert.rejects()` for testing and | ||
comparison. | ||
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The `expected` argument can be an Error Object (instance), an Error Function | ||
(constructor), a RegExp that matches (or partially matches) the String | ||
representation, or a callback Function that must return `true` to pass the | ||
assertion check. | ||
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### Example | ||
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Assert the correct error message is received for a custom error object. | ||
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```js | ||
QUnit.test( "rejects", function( assert ) { | ||
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function CustomError( message ) { | ||
this.message = message; | ||
} | ||
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CustomError.prototype.toString = function() { | ||
return this.message; | ||
}; | ||
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assert.rejects( | ||
Promise.reject("error"), | ||
"rejects with just a message, not using the 'expected' argument" | ||
); | ||
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assert.rejects( | ||
Promise.reject(new CustomError("some error description")), | ||
/description/, | ||
"raised error message contains 'description'" | ||
); | ||
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assert.rejects( | ||
Promise.reject(new CustomError()), | ||
CustomError, | ||
"raised error is an instance of CustomError" | ||
); | ||
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assert.rejects( | ||
Promise.reject(new CustomError("some error description")), | ||
new CustomError("some error description"), | ||
"raised error instance matches the CustomError instance" | ||
); | ||
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assert.rejects( | ||
Promise.reject(throw new CustomError("some error description")), | ||
function( err ) { | ||
return err.toString() === "some error description"; | ||
}, | ||
"raised error instance satisfies the callback function" | ||
); | ||
}); | ||
``` |