Test a rejection with Chai as promised

Having version 5.1.0 of ChaiAsPromised, solution from Keithamus did not work for me - rejectedWith did not gave me the error object to assert, but "rejected" did:

return expect(foo())
    .to.be.rejected
    .and.be.an.instanceOf(Error)
    .and.have.property('code', 'EFOO');

For asserting multiple properties

return expect(foo())
    .to.be.rejected
    .then(function(error) {
        expect(error).to.have.property('name', 'my error message');
        expect(error).to.have.property('code', 'EFOO');
    });

If you're using Chai-As-Promised (as you say you are), then it allows for chaining off of rejectedWith - and it sets the chain assertion object to be the error object - meaning anything after rejectedWith() is now going to assert on the Error. This lets you do cool things like:

return expect(foo()).to.eventually
  .be.rejectedWith("my error message")
  .and.be.an.instanceOf(Error)
  .and.have.property('code', 'EFOO');

Some of the chai methods also chain, so you can use that to make some quite deeply nested assertions about the error:

return expect(foo()).to.eventually
  .be.rejectedWith("my error message")
  .and.have.property('stack')
    .that.includes('myfile.js:30')