This test fails intermittently on my machine, but I don't know what triggers it:
```
Traceback (most recent call last):
  File "/Users/jvkersch/Desktop/Enthought/traits-enaml/traits_enaml/testing/tests/test_gui_test_assistant.py", line 104, in test_event_loop_until_trait_change
    deferred_call(self._set_trait, 5.0)
  File "/Applications/Canopy.app/appdata/canopy-1.3.0.1715.macosx-x86_64/Canopy.app/Contents/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/Users/jvkersch/Desktop/Enthought/traits-enaml/traits_enaml/testing/gui_test_assistant.py", line 207, in event_loop_until_traits_change
    yield
  File "/Applications/Canopy.app/appdata/canopy-1.3.0.1715.macosx-x86_64/Canopy.app/Contents/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/Users/jvkersch/Desktop/Enthought/traits-enaml/traits_enaml/testing/gui_test_assistant.py", line 122, in event_loop_until_condition
    self.fail('Timed out waiting for condition')
AssertionError: Timed out waiting for condition
```