Testing functions that return Promises in Mocha

mocha-test-promises.js

// Basic verification
// Returns the promise from somethingAsync()
// The test passes if resolved, fails if rejected

it('does something async with promises', function() {
  return somethingAsync();
});

// Verify a fulfilled promise
// Returns the promise from somethingAsync() and runs assertions in the onFulfilled callback
// If an assertion fails, a rejected promise is returned and the test fails

it('does something async with promises', function() {
  return somethingAsync().then(function fulfilled(result) {
    assert(...)
  });
});

// Verify a rejected promise
// Returns the promise from somethingAsync() and runs assertions in the onRejected callback
// If the promise resolves, an error is thrown and the test fails
// If an assertion fails, a rejected promise is returned and the test fails

it('returns rejected promise on bad input', function() {
  return somethingAsync('bad input').then(function fulfilled(result) {
    throw new Error('Promise was unexpectedly fulfilled. Result: ' + result);
  }, function rejected(error) {
    assert(...)
  });
});