CI can't catch a missing Colab clone cell — add a static check (tests/test_colab_clone_cell.py)

[kwlee2025cpp]

Problem

A notebook that imports an nmisp_py helper (import matshow, jacobi, matrix, gauss_jordan, …) must include the Google Colab clone cell, or it fails at import in Colab. CI does not catch this:

• the test jobs run nbconvert --execute in the repo checkout, where the helper .py files sit next to the notebooks → the import always resolves locally;
• the clone cell's if 'google.colab' in str(get_ipython()) guard is False on a GitHub runner → the clone path is never exercised;
• test_ipynb_colab only swaps in Colab dependency versions, not Colab's standalone import environment.

Concrete example

60_linear_algebra_2/220_Google_PageRank.ipynb imported matshow but had no clone cell — green in CI, broken in Colab — until it was added manually.

Proposed fix: a fast static test (no execution) — tests/test_colab_clone_cell.py

"""A notebook importing an nmisp_py helper must include the Colab clone cell."""
import json, pathlib, re, pytest
REPO = pathlib.Path(__file__).resolve().parents[1]
EXCLUDE = {'tests', 'utils', 'build_util', '.ipynb_checkpoints'}
HELPERS = {p.stem for p in REPO.rglob('*.py')
           if not (set(p.relative_to(REPO).parts) & EXCLUDE) and p.stem != '__init__'}
NOTEBOOKS = [p for p in REPO.rglob('*.ipynb')
             if not (set(p.relative_to(REPO).parts) & EXCLUDE)]

@pytest.mark.parametrize('nb', NOTEBOOKS, ids=lambda p: str(p.relative_to(REPO)))
def test_helper_import_has_colab_clone_cell(nb):
    code = '\n'.join(''.join(c['source']) for c in json.loads(nb.read_text())['cells']
                     if c['cell_type'] == 'code')
    used = sorted(({*re.findall(r'^\s*import\s+(\w+)', code, re.M),
                    *re.findall(r'^\s*from\s+(\w+)\s+import', code, re.M)} & HELPERS))
    if used:
        assert 'google.colab' in code, \
            f"{nb.name} imports nmisp_py helper(s) {used} but has no Colab clone cell"

• Runs inside the existing pytest ./tests invocation, sub-second, one clear failure per offending notebook.
• Passes today (repo is clean after the recent fixes) and would have caught the 220 regression.

Related

• CI: 030_Classification_Optimization kills the CI kernel and gates the nmisp_py auto-sync #440 — 030 dead-kernel gates test_ipynb_colab and the nmisp_py auto-sync.
• CI blind spot: interactive ipywidgets callbacks aren't exercised (slider-state bugs slip through) #441 — CI can't exercise interactive ipywidgets callbacks.

Same theme: CI tests the repo, non-interactive path, not the Colab standalone path.

🤖 Filed via Claude Code.