Building Enterprise JavaScript Applications

Dealing with rejected promises

However, another limitation of Mocha is that you cannot return a rejected promise inside the hook functions. If you do, Mocha will think the test has failed. In those cases, you should move the function that you expect to fail inside the it block, and make any assertions inside a catch block:

it('should fail', function() {  createUser(...)    .catch(actualError => assert(actualError, expectedError))});