title: Karma passes test when promise is rejected during assertion
body: <p>If the promise itself is rejected as in the <code>'does fail'</code> test, then the test fails as I would expect.  If an assertion fails/error is thrown/promise is rejected in the "then" of the promise I get logging saying <code>ERROR: 'Unhandled promise rejection'</code> and the test passes anyway.  How do I get it to fail on rejection rather than log that the rejection was unhandled?</p>
  
  <pre><code>import { expect } from 'chai';
  
  describe.only('What?', () =&gt; {
    const e = new Error('NOPE');
  
    it('does fail', () =&gt; Promise.reject(e));
  
    it('should fail when rejected', () =&gt; {
      const promise = new Promise(r =&gt; r());
  
      promise.then(() =&gt; Promise.reject(e));
  
      return promise;
    });
  
    it('should fail when thrown, then caught then rejected', () =&gt; {
      const promise = new Promise(r =&gt; r());
  
      promise
        .then(() =&gt; { throw e; })
        .catch(() =&gt; Promise.reject('huh'));
  
      return promise;
    });
  
    it('should fail/reject when thrown, then caught then rethrown', () =&gt; {
      const promise = new Promise(r =&gt; r());
  
      promise
        .then(() =&gt; { throw e; })
        .catch(er =&gt; { throw er; });
  
      return promise;
    });
  
    it(`doesn't matter if I expect`, () =&gt; {
      const promise = new Promise(r =&gt; r());
  
      promise.then(() =&gt; {
        expect(1).to.eq(2);
      });
  
      return promise;
    });
  });
  </code></pre>
  
  <p>Which then reports...</p>
  
  <pre><code>START:
    What?
      ✖ does fail
      ✔ should fail when rejected
  ERROR: 'Unhandled promise rejection', Error{stack: undefined}
      ✔ should fail when thrown, then caught then rejected
  ERROR: 'Unhandled promise rejection', 'huh'
      ✔ should fail/reject when thrown, then caught then rethrown
  ERROR: 'Unhandled promise rejection', Error{stack: undefined, line: 47567, sourceURL: 'http://localhost:9876/base/test/test_index.js?7f696b0b50c0a51c7a2fa5278582072b20241a3b'}
      ✔ doesn't matter if I expect
  ERROR: 'Unhandled promise rejection', AssertionError{message: 'expected 1 to equal 2', showDiff: true, actual: 1, expected: 2, stack: 'AssertionError@http://localhost:9876/base/test/test_index.js?7f696b0b50c0a51c7a2fa5278582072b20241a3b:39222:25
  </code></pre>