Improve test coverage slightly #255

Job	Run time
test (stable)	23s
test (beta)	22s
clippy	19s
test (nightly-2023-04-01)	24s
build (stable)	20s
examples (stable)	13s
build (beta)	19s
examples (beta)	20s
formatting	51s
build (nightly-2023-04-01)	22s
examples (nightly-2023-04-01)	22s
Rust 1.58.0 MSRV	1m 19s
Rust 1.59.0 MSRV	1m 16s
Build for a no_std target (stable)	18s
Build for a no_std target (beta)	19s
coverage	2m 10s
Build for a no_std target (nightly-2023-04-01)	21s
deny	3m 32s
doc	16s
udeps	4m 11s
	17m 57s

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