Add tests, update CI and README

[jlapeyre]

• Add a couple of tests
• Fix some bitrot

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (f952293) to head (7e75382).
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##           master       #10       +/-   ##
============================================
+ Coverage   85.00%   100.00%   +15.00%     
============================================
  Files           1         1               
  Lines          20        20               
============================================
+ Hits           17        20        +3     
+ Misses          3         0        -3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.