test: add tests to catch 2 mutants #686

Job	Run time
Check	20s
Clippy	33s
Code coverage	1m 30s
Documentation	17s
Rustfmt	12s
Check with minimal Rust version	54s
Test all features	41s
Mutation tests (0)	2m 39s
Test feature alpha-async-tokio-rusqlite	50s
Mutation tests (1)	2m 26s
Test examples	46s
Test feature from-directory	38s
Mutation tests (2)	2m 12s
Mutation tests (3)	2m 15s
Test no features	44s
Mutation tests (4)	2m 24s
Mutation tests (5)	2m 25s
Mutation tests (6)	2m 28s
Mutation tests (7)	2m 17s
	26m 31s

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