add a test for `create_library`

[KristofferC]

Fixes #613, don't think it will pass on Windows, might have to adjust CI for that?

[codecov[bot]]

Codecov Report

Merging #614 (e2bbf3b) into master (7bbf5a0) will decrease coverage by 21.92%. The diff coverage is n/a.

:exclamation: Current head e2bbf3b differs from pull request most recent head d018b7d. Consider uploading reports for the commit d018b7d to get more accurate results

@@             Coverage Diff             @@
##           master     #614       +/-   ##
===========================================
- Coverage   95.32%   73.39%   -21.93%     
===========================================
  Files           2        2               
  Lines         449      436       -13     
===========================================
- Hits          428      320      -108     
- Misses         21      116       +95     

Impacted Files	Coverage Δ
src/juliaconfig.jl	48.88% <ø> (-41.81%)	:arrow_down:
src/PackageCompiler.jl	76.21% <0.00%> (-19.60%)	:arrow_down:

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