to call the callback without error

• <function> to call the callback without error

Asserts that a node.js-style asynchronous function taking a single callback will call it without passing a truthy value as the first parameter.

function mySuccessfulAsyncFunction(cb) {
  setTimeout(cb, 0);
}
 
return expect(mySuccessfulAsyncFunction, 'to call the callback without error');

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

function myFailingAsyncFunction(cb) {
  setTimeout(function () {
    cb(new Error('Oh dear'));
  }, 0);
}
 
return expect(myFailingAsyncFunction, 'to call the callback without error');

expected
function myFailingAsyncFunction(cb) {
  setTimeout(function () {
    cb(new Error('Oh dear'));
  }, 0);
}
to call the callback without error
  
called the callback with: Error('Oh dear')

The parameters passed to the callback (excluding the falsy error) are also provided as the value of the returned promise, so you can do further assertions like this:

function asyncFn(cb) {
  cb(null, 123, 456);
}

return expect(asyncFn, 'to call the callback without error').then(function (
  args
) {
  // args will be [123, 456];
});

Or using the Bluebird-specific .spread extension:

return expect(asyncFn, 'to call the callback without error').spread(function (
  result1,
  result2
) {
  // result1 will be 123
  // result2 will be 456
});