test: add tests to catch 2 mutants #691

Job	Run time
Test feature alpha-async-tokio-rusqlite	46s
Check	16s
Documentation	11s
Rustfmt	8s
Clippy	16s
Check with minimal Rust version	53s
Mutation tests (0)	1m 28s
Test all features	42s
Mutation tests (1)	1m 30s
Test examples	53s
Mutation tests (2)	1m 24s
Test feature from-directory	47s
Mutation tests (3)	1m 26s
Test no features	44s
Code coverage	1m 29s
	12m 53s

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