test: add tests to catch 2 mutants #685

Job	Run time
Clippy	11s
Code coverage	1m 23s
Documentation	12s
Check	17s
Rustfmt	10s
Check with minimal Rust version	53s
Mutation tests (0)	2m 51s
Test all features	49s
Mutation tests (1)	2m 57s
Test feature alpha-async-tokio-rusqlite	46s
Test examples	47s
Mutation tests (2)	2m 27s
Mutation tests (3)	2m 18s
Test feature from-directory	47s
Test no features	45s
Mutation tests (4)	2m 19s
Mutation tests (5)	2m 18s
Mutation tests (6)	2m 17s
Mutation tests (7)	2m 27s
	26m 54s

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