test: unify assertSnapshot common patterns #2856

Job	Run time
Build slim tarball	1m 23s
aarch64-darwin: with shared libraries	2h 18m 32s
aarch64-linux: with shared libraries	1h 25m 46s
x86_64-darwin: with shared libraries	1h 4m 55s
x86_64-linux: with shared libraries	2h 2m 32s
	6h 53m 8s

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