More tests

[zfergus]

Description

Add more tests to improve code coverage, and fix small bugs.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have followed the project style guide
• My code follows the clang-format style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Merging #65 (0154f4d) into main (cea3f91) will increase coverage by 3.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
+ Coverage   87.18%   90.34%   +3.15%     
==========================================
  Files          81       82       +1     
  Lines        7267     7250      -17     
==========================================
+ Hits         6336     6550     +214     
+ Misses        931      700     -231     

Files	Coverage Δ
src/ipc/candidates/candidates.cpp	91.86% <100.00%> (+8.94%)	⬆️
src/ipc/collision_mesh.cpp	99.54% <100.00%> (+5.00%)	⬆️
src/ipc/collisions/plane_vertex.cpp	100.00% <100.00%> (ø)
src/ipc/collisions/plane_vertex.hpp	100.00% <ø> (+100.00%)	⬆️
src/ipc/friction/closest_point.cpp	100.00% <ø> (+6.71%)	⬆️

... and 11 files with indirect coverage changes