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Called each time a MavericksViewModel.execute function is invoked. This allows the execute function to be skipped, based on the returned BlockExecutions value.
This is intended to be used to allow the ViewModel to be mocked out for testing. Blocking calls to execute prevents long running asynchronous operations from changing the state later on when the calls complete.
Mocking out the state store cannot accomplish this on its own, because in some cases we may want the state store to initially be mocked, with state changes blocked, but later on we may want it to allow state changes.
This prevents the case of an executed async call from modifying state once the state stored is "enabled", even if the execute was performed when the state store was "disabled" and we didn't intend to allow operations to change the state.