Behave like Base wrt. test flags.

[maleadt]

Fixes #182

[codecov]

Codecov Report

Merging #184 into master will decrease coverage by 0.22%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #184      +/-   ##
==========================================
- Coverage   80.92%   80.69%   -0.23%     
==========================================
  Files         142      142              
  Lines        9137     9134       -3     
==========================================
- Hits         7394     7371      -23     
- Misses       1743     1763      +20     

Impacted Files	Coverage Δ
test/runtests.jl	50.34% <100.00%> (-10.92%)	⬇️
lib/cuda/occupancy.jl	94.44% <0.00%> (-5.56%)	⬇️
deps/bindeps.jl	81.94% <0.00%> (-2.09%)	⬇️

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