add unittests and improve several type checkings

[houpc]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 96.17225% with 24 lines in your changes missing coverage. Please review.

Project coverage is 78.22%. Comparing base (2166f30) to head (c112593).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
src/integrators_test.py	94.22%	13 Missing ⚠️
src/maps_test.py	96.79%	5 Missing ⚠️
src/maps.py	78.94%	4 Missing ⚠️
src/base_test.py	98.68%	1 Missing ⚠️
src/utils_test.py	99.15%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #10       +/-   ##
===========================================
+ Coverage   54.80%   78.22%   +23.41%     
===========================================
  Files           9       13        +4     
  Lines         967     1575      +608     
===========================================
+ Hits          530     1232      +702     
+ Misses        437      343       -94     

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