Tests

Optimize a bit, test more, and document more #3

Job	Run time
test-cross-platform (macos-latest, 22.x)	9s
test-cross-platform (windows-latest, 22.x)	31s
test (20.x)	6s
test (16.x)	9s
test (18.x)	7s
test (24.x)	10s
test (22.x)	13s
	1m 25s

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