[MAINT] Rename and move testing utilities under tests directory in each module

[ymzayek]

• Closes Homogenize location and naming of testing utilities #4046

Changes proposed in this pull request:

• Testing utilities are now under tests/_testing.py in each module where they exist. Happy to change the name but I didn't use any version of "utils" because there are utils.py files that are relevant to the module functionality as opposed to the testing and where they exist they are usually tested in tests/test_utils.py

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[codecov]

Codecov Report

Merging #4047 (8e3cd8c) into main (c018480) will decrease coverage by 0.04%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #4047      +/-   ##
==========================================
- Coverage   91.59%   91.56%   -0.04%     
==========================================
  Files         145      143       -2     
  Lines       16238    16057     -181     
  Branches     3376     3332      -44     
==========================================
- Hits        14874    14703     -171     
+ Misses        817      811       -6     
+ Partials      547      543       -4     

Flag	Coverage Δ
macos-latest_3.10	91.48% <100.00%> (-0.04%)	⬇️
macos-latest_3.11	91.48% <100.00%> (-0.04%)	⬇️
macos-latest_3.12	91.48% <100.00%> (-0.04%)	⬇️
macos-latest_3.8	91.44% <100.00%> (-0.04%)	⬇️
macos-latest_3.9	91.45% <100.00%> (-0.04%)	⬇️
ubuntu-latest_3.10	91.48% <100.00%> (-0.04%)	⬇️
ubuntu-latest_3.11	91.48% <100.00%> (-0.04%)	⬇️
ubuntu-latest_3.12	91.48% <100.00%> (-0.04%)	⬇️
ubuntu-latest_3.8	91.44% <100.00%> (-0.04%)	⬇️
ubuntu-latest_3.9	91.45% <100.00%> (-0.04%)	⬇️
windows-latest_3.10	91.43% <100.00%> (-0.04%)	⬇️
windows-latest_3.11	91.43% <100.00%> (?)
windows-latest_3.12	91.43% <100.00%> (-0.04%)	⬇️
windows-latest_3.8	91.38% <100.00%> (-0.04%)	⬇️
windows-latest_3.9	91.39% <100.00%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
nilearn/interfaces/fmriprep/tests/_testing.py	98.50% <ø> (ø)
...n/interfaces/fmriprep/tests/test_load_confounds.py	98.40% <100.00%> (ø)
...s/fmriprep/tests/test_load_confounds_components.py	100.00% <100.00%> (ø)
...ces/fmriprep/tests/test_load_confounds_strategy.py	100.00% <100.00%> (ø)
...rfaces/fmriprep/tests/test_load_confounds_utils.py	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[Remi-Gau]

What's you take on this one: https://github.com/nilearn/nilearn/blob/main/nilearn/_utils/testing.py ?

I suspect it is in a private module and contains testing utilities used for several other modules so it is fine where it is and named as it is. Just want to make sure we are on the same page.

[ymzayek]

What's you take on this one: https://github.com/nilearn/nilearn/blob/main/nilearn/_utils/testing.py ?

I suspect it is in a private module and contains testing utilities used for several other modules so it is fine where it is and named as it is. Just want to make sure we are on the same page.

Yes that's what I was thinking too. It doesn't fit the pattern of the others that are private to the testing of a specific module (with one or two functions being an exception like the generate_surf in nilearn/surface/tests/_testing being used in plotting/tests/test_surf_plotting)

[Remi-Gau]

OK we agree on this. Good to me then. Let's merge.

Thanks for taking care of this. This one has been itching my inner Marie Kondo for a while.