Add tests for event_handler #84

Job	Run time
pytest / setup	2s
pytest / pytest (macos-latest, 3.8)	1m 25s
pytest / pytest (macos-latest, 3.9)	56s
pytest / pytest (macos-latest, 3.10)	56s
pytest / pytest (macos-latest, 3.11)	45s
pytest / pytest (macos-latest, 3.12)	44s
pytest / pytest (ubuntu-22.04, 3.8)	1m 20s
pytest / pytest (ubuntu-22.04, 3.9)	4m 15s
pytest / pytest (ubuntu-22.04, 3.10)	1m 22s
pytest / pytest (ubuntu-22.04, 3.11)	1m 20s
pytest / pytest (ubuntu-22.04, 3.12)	1m 19s
pytest / pytest (windows-latest, 3.8)	2m 1s
pytest / pytest (windows-latest, 3.9)	2m 20s
pytest / pytest (windows-latest, 3.10)	2m 15s
pytest / pytest (windows-latest, 3.11)	2m 24s
pytest / pytest (windows-latest, 3.12)	1m 58s
pytest / pytest (ubuntu-20.04, 3.6)	48s
	26m 10s

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