tests: test functions with random signatures

[mmcloughlin]

Updates #191 #195

[codecov-commenter]

Codecov Report

Merging #216 (49bde13) into master (bcbebd5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #216   +/-   ##
=======================================
  Coverage   75.64%   75.64%           
=======================================
  Files          57       57           
  Lines       35132    35132           
=======================================
  Hits        26577    26577           
  Misses       8402     8402           
  Partials      153      153           

Flag	Coverage Δ
integration	8.81% <ø> (ø)
unittests	73.30% <ø> (ø)

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