dominoes: make test code more idiomatic (#2127) #3108

Job	Run time
Clippy	1m 15s
Check Rust Formatting	24s
Run shellcheck on scripts	5s
markdown lint	13s
configlet lint	5s
Check compilation (stable)	1m 31s
Check exercises on nightly (benchmark enabled)	48s
Run repository tests	55s
Check compilation (beta)	1m 25s
	6m 41s

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