Typical lifecycle of PatternTestState:

• The PatternTestController creates a PatternTestState for the PatternTest to be executed.
• The controller populates the test state with slot binding accessors for each PatternTestParameter associated with the test.
• The controller calls BeforeTestChain to give test extensions the opportunity to modify the test state.
• The controller begins iterating over the IDataItems produced by the state's BindingContext. For each item it constructs a PatternTestInstanceState and executes the test instance.
• The controller calls AfterTestChain to give test extensions the opportunity to clean up the test state.