Improve type-checking of imports

[jwodder]

No description provided.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.80%. Comparing base (b88f21a) to head (5ae8de1).
Report is 80 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #179      +/-   ##
==========================================
- Coverage   65.06%   64.80%   -0.27%     
==========================================
  Files           1        1              
  Lines        1500     1500              
  Branches      346      346              
==========================================
- Hits          976      972       -4     
- Misses        429      431       +2     
- Partials       95       97       +2     

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[yarikoptic]

not familiar with this syntax, could you please digest it for me?

[jwodder]

This is tox-specific syntax that causes all deps listed in the [testenv] environment (i.e., all of our test dependencies) to be included in the deps for the typing environment. This is necessary for mypy to be able to type-check test code that uses dependencies like pytest.