[MRG] Add download flag for get_testdata_file

[orsinium]

Describe the changes

Allow specifying the download=False flag for get_testdata_file to make sure the function doesn't send any network requests.

Tasks

• Unit tests added that reproduce the issue or prove feature is working
• Fix or feature added
• Code typed and mypy shows no errors
• Documentation updated (if relevant)
  • No warnings during build
  • Preview link (CircleCI -> Artifacts -> doc/_build/html/index.html)
• Unit tests passing and overall coverage the same or better

[codecov]

Codecov Report

Merging #1617 (1d6c7d0) into master (07aea31) will decrease coverage by 9.41%.
The diff coverage is 86.66%.

@@            Coverage Diff             @@
##           master    #1617      +/-   ##
==========================================
- Coverage   97.56%   88.14%   -9.42%     
==========================================
  Files          66       66              
  Lines       10646    10420     -226     
==========================================
- Hits        10387     9185    -1202     
- Misses        259     1235     +976     

Impacted Files	Coverage Δ
pydicom/data/data_manager.py	84.61% <85.71%> (-15.39%)	⬇️
pydicom/sr/coding.py	100.00% <100.00%> (ø)
pydicom/pixel_data_handlers/util.py	17.93% <0.00%> (-82.07%)	⬇️
pydicom/waveforms/numpy_handler.py	20.31% <0.00%> (-79.69%)	⬇️
pydicom/encoders/gdcm.py	20.96% <0.00%> (-75.81%)	⬇️
pydicom/pixel_data_handlers/numpy_handler.py	27.14% <0.00%> (-72.86%)	⬇️
pydicom/pixel_data_handlers/gdcm_handler.py	26.22% <0.00%> (-66.46%)	⬇️
pydicom/overlays/numpy_handler.py	35.18% <0.00%> (-64.82%)	⬇️
pydicom/pixel_data_handlers/pillow_handler.py	31.73% <0.00%> (-64.43%)	⬇️
pydicom/pixel_data_handlers/rle_handler.py	36.97% <0.00%> (-63.03%)	⬇️
... and 17 more

📣 Codecov can now indicate which changes are the most critical in Pull Requests. Learn more

[pep8speaks]

Hello @orsinium! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2022-03-22 06:58:19 UTC

[mrbean-bremen]

Thanks! Didn't you remove that ignore to shut up the type checker, or have I dreamed this?

[orsinium]

Didn't you remove that ignore to shut up the type checker, or have I dreamed this?

I don't remember 🙃 But I can do it, why not.

[mrbean-bremen]

I don't remember 🙃 But I can do it, why not.

Just noticed that this was actually done in another PR... but thanks!

@darcymason - can you have a quick look?