* Add format command to makefile
* Refactor executions to be a attribute of StateMachine
* Begin to add tests for execution history
* Add tests for failed and successful event histories, with implementations
* Add failure case to environment var check
* Skip test if in server mode and update implementation coverage
* Add conditional import for mock to cover python 2
* Refactor stop execution logic into StateMachine
* Refactor event history environment variable into settings.py
* Remove typing and os import
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