Function rejects

Awaits the asyncFn promise or, if asyncFn is a function, immediately calls the function and awaits the returned promise to complete. It will then check that the promise is rejected.

If asyncFn is a function and it throws an error synchronously,assert.rejects() will return a rejected Promise with that error. If the function does not return a promise, assert.rejects() will return a rejectedPromise with an ERR_INVALID_RETURN_VALUE error. In both cases the error handler is skipped.

Besides the async nature to await the completion behaves identically to throws.

If specified, error can be a Class, RegExp, a validation function, an object where each property will be tested for, or an instance of error where each property will be tested for including the non-enumerable message andname properties.

If specified, message will be the message provided by the AssertionError if the asyncFn fails to reject.

import assert from 'assert/strict';

await assert.rejects(
  async () => {
    throw new TypeError('Wrong value');
  },
  {
    name: 'TypeError',
    message: 'Wrong value'
  }
);

import assert from 'assert/strict';

await assert.rejects(
  async () => {
    throw new TypeError('Wrong value');
  },
  (err) => {
    assert.strictEqual(err.name, 'TypeError');
    assert.strictEqual(err.message, 'Wrong value');
    return true;
  }
);

import assert from 'assert/strict';

assert.rejects(
  Promise.reject(new Error('Wrong value')),
  Error
).then(() => {
  // ...
});

error cannot be a string. If a string is provided as the second argument, then error is assumed to be omitted and the string will be used formessage instead. This can lead to easy-to-miss mistakes. Please read the example in throws carefully if using a string as the second argument gets considered.