dominoes: make test code more idiomatic #3102

Job	Run time
markdown lint	14s
Check Rust Formatting	22s
Check compilation (beta)	17s
Run shellcheck on scripts	4s
Clippy	15s
Check exercises on nightly (benchmark enabled)	18s
configlet lint	5s
Run repository tests	1m 0s
Check compilation (stable)	14s
	2m 49s

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