Improve test coverage slightly #253

Job	Run time
coverage	2m 5s
deny	3m 30s
build (stable)	20s
clippy	16s
build (beta)	21s
doc	18s
build (nightly-2023-04-01)	21s
examples (stable)	19s
formatting	1m 4s
examples (beta)	19s
Rust 1.58.0 MSRV	1m 22s
examples (nightly-2023-04-01)	23s
Rust 1.59.0 MSRV	1m 17s
Build for a no_std target (stable)	19s
test (stable)	24s
test (beta)	21s
Build for a no_std target (beta)	18s
udeps	4m 35s
test (nightly-2023-04-01)	55s
Build for a no_std target (nightly-2023-04-01)	21s
	19m 8s

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