Use pytest for testing.

[lincmba]

• Update tests
• Update documentation
• Update requirements
• Update CI workflow

[codecov-commenter]

Codecov Report

Merging #423 (9802200) into master (cdff759) will increase coverage by 0.82%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #423      +/-   ##
==========================================
+ Coverage   70.16%   70.98%   +0.82%     
==========================================
  Files         139      139              
  Lines        9220     9220              
==========================================
+ Hits         6469     6545      +76     
+ Misses       2751     2675      -76     

see 8 files with indirect coverage changes

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