$ python machine_spec.py
test_MachineShouldInitiallyHaveStateOfTheFirstState (__main__.machine_spec) ... ok
test_MachineShouldRememberListOfEventsWithTransitions (__main__.machine_spec) ... ok
test_MachineShouldRememberListOfValidStates (__main__.machine_spec) ... ok
test_MachineShouldTransitionToCheckingOutUponTriggerCheckOutEvent (__main__.machine_spec) ... ERROR

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ERROR: test_MachineShouldTransitionToCheckingOutUponTriggerCheckOutEvent (__main__.machine_spec)
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Traceback (most recent call last):
  File "machine_spec.py", line 27, in test_MachineShouldTransitionToCheckingOutUponTriggerCheckOutEvent
    self.machine.trigger( 'CheckOut' )
AttributeError: Machine instance has no attribute 'trigger'

----------------------------------------------------------------------
Ran 4 tests in 0.011s

FAILED (errors=1)
$