#5: Add a test suite

[btreeby]

Add automated test suite and CI

Summary

Adds a MATLAB matlab.unittest test suite for the toolbox and wires it up to GitHub Actions so every push and PR runs the tests automatically.

Closes #5

What's in this PR

• Unit tests (tests/unit/, 33 tests) covering the pure helpers in +petraToCT/+tools/ (radius2measure, getLargestCC, fillAllHoles, fillSmallHoles, applyHUMapping) and the histogram normalisation. All run in seconds and need no external tools or data.

• Integration tests (tests/integration/, 4 tests) exercising debias, segmentationSPM, and the full convert pipeline against a small defaced PETRA fixture at tests/fixtures/petra.nii.gz. Gated with assumeTrue so they filter (not fail) when SPM or 3D Slicer aren't available. Intended for local pre-release runs; they report as filtered in CI.

• Small refactor: extracted the hard-coded HU calibration (-1000 / 42 / -2929.6 * x + 3274.9) from convert.m into a new pure helper +petraToCT/+tools/applyHUMapping.m so the calibration numbers can be pinned by a unit test.

• GitHub Actions workflow (.github/workflows/ci.yml) running the suite on ubuntu-latest with matlab-actions/setup-matlab@v3 (Image Processing + Signal Processing toolboxes) on every push to main and every PR.

• README updated with a CI badge and a ## Testing section documenting how to run the suite locally.

Test plan

• runtests("tests", IncludeSubfolders=true) passes locally (33 unit + 4 integration = 37 tests).
• CI run on this branch is green — unit tier passes, integration tier filters correctly.
• After merge, enable a branch protection rule on main requiring the MATLAB tests check.

Notes

• The fixture (tests/fixtures/petra.nii.gz, 4.6 MB) is a defaced, 2 mm isotropic PETRA volume. Generation pipeline is documented in tests/fixtures/README.md.
• Integration tests are slow (~15-20 min each for SPM) and intentionally run only locally.