Mocha and generators (2)

I've blogged before about this topic and I had a problem when it comes to test exceptions.
The problem is caused by Promise.spawn which returns a promise and swallow all errors thrown inside. To still get a failing test if an unexpected error is thrown, the following form should be used:

test('everything is good', function(done) {
  Promise.spawn(function* () {
    assert.equal(foo, 'true'); // foo is undefined
  }).catch(done); // ** note this line **

Et voila, this test will fail as expected.