to call the callback with error

• <function> to call the callback with error <any>
• <function> to call the callback with error

Asserts that a node.js-style asynchronous function taking a single callback will call it with a truthy value as the first parameter.

function myFailingAsyncFunction(cb) {
  setTimeout(function () {
    cb(new Error('Oh dear'));
  }, 0);
}

return expect(myFailingAsyncFunction, 'to call the callback with error');

You can assert the error message is a given string if you provide a string as the second parameter.

return expect(
  myFailingAsyncFunction,
  'to call the callback with error',
  'Oh dear'
);

A regular expression, Error instance, or an object will also work, as the matching uses to satisfy semantics:

return expect(
  myFailingAsyncFunction,
  'to call the callback with error',
  /dear/
);

In case of a failing expectation you get the following output:

return expect(
  myFailingAsyncFunction,
  'to call the callback with error',
  new Error('foo')
);

expected
function myFailingAsyncFunction(cb) {
  setTimeout(function () {
    cb(new Error('Oh dear'));
  }, 0);
}
to call the callback with error Error('foo')
  
expected Error('Oh dear') to satisfy Error('foo')
 
Error({
  
message: 
'Oh dear'
 
//
//
//
//
 
should equal 
'foo'
 
Oh dear
foo
})

The error passed to the callback is also provided as the fulfillment value of the returned promise, so you can do further assertions like this:

function asyncFn(cb) {
  cb(new Error('yikes'));
}
 
return expect(asyncFn, 'to call the callback with error').then(function (err) {
  // err will be new Error('yikes')
  expect(err, 'to have message', 'yikes');
});