CONTRIBUTING.md references wrong test directory 'test/' instead of 'tests/'

[anxkhn]

Context

The CONTRIBUTING.md file tells contributors to run tests with pytest test/ -v, but the actual test directory is named tests/ (with an "s"). This causes confusion and command failures for new contributors following the guide.

Steps to reproduce

1. Open CONTRIBUTING.md.
2. Find the test commands in sections "Getting Started" (step 4) and "Making Changes" (step 3).
3. Both say pytest test/ -v.
4. Run: pytest test/ -v -- this fails because the directory does not exist.

Expected behavior

The commands should reference the correct directory: pytest tests/ -v.

Actual behavior

The commands reference pytest test/ -v which does not exist.

Files

• CONTRIBUTING.md -- two occurrences of pytest test/ -v

Acceptance criteria

• Both occurrences of pytest test/ in CONTRIBUTING.md are changed to pytest tests/
• The commands work correctly when copy-pasted by a contributor

Suggested approach

1. Open CONTRIBUTING.md.
2. Find and replace pytest test/ with pytest tests/ (there are 2 occurrences).
3. Verify by reading through the file that the instructions make sense.