test: minor cleanup

[ofrobots]

Obsessive compulsive.

[codecov-io]

Codecov Report

Merging #170 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #170      +/-   ##
==========================================
- Coverage   97.23%   97.21%   -0.03%     
==========================================
  Files          10       10              
  Lines         398      395       -3     
  Branches       28       28              
==========================================
- Hits          387      384       -3     
  Misses         11       11

Impacted Files	Coverage Δ
test/test-clean.ts	100% <100%> (ø)	⬆️
test/test-format.ts	100% <100%> (ø)	⬆️
test/test-lint.ts	100% <100%> (ø)	⬆️

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[ofrobots]

TBR=@jinwoo

[jinwoo]

Personally I prefer having async/await even though they are redundant. That's because it makes it easy to know there's async stuff going on there without looking up the return type of withFixtures. But that's a personal preference. So LGTM.