Add Macros for Testability

[Stuart Scott]

The addition of some ASSERT_ macros would help make the tests more readable;

• assert counter (#45):
  • assert onEntry counter
  • assert onExit counter
  • assert receiver(message) counter
• assert state transition
• assert message was sent
• assert child was spawned

[Wink Saville]

Should the title be "Add Macros for Testability"?