adding testing instructions

[djarecka]

• adding testing instruction to DEVELOPMENT.md

[codecov]

Codecov Report

Base: 87.90% // Head: 87.74% // Decreases project coverage by -0.16% ⚠️

Coverage data is based on head (1859ea6) compared to base (a508e63).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1123      +/-   ##
==========================================
- Coverage   87.90%   87.74%   -0.17%     
==========================================
  Files          73       73              
  Lines        8549     8549              
==========================================
- Hits         7515     7501      -14     
- Misses       1034     1048      +14     

Flag	Coverage Δ
unittests	87.74% <ø> (-0.17%)	⬇️

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Impacted Files	Coverage Δ
dandi/support/tests/test_iterators.py	94.73% <0.00%> (-5.27%)	⬇️
dandi/tests/skip.py	84.37% <0.00%> (-4.69%)	⬇️
dandi/_version.py	44.21% <0.00%> (-1.76%)	⬇️
dandi/tests/fixtures.py	96.92% <0.00%> (-1.16%)	⬇️
dandi/utils.py	81.90% <0.00%> (-0.31%)	⬇️

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[djarecka]

@jwodder - do you want me to change something else? or can we merge it?

[github-actions]

🚀 PR was released in 0.46.6 🚀