Add Python test coverage and extend unit tests

- Add make test-python-coverage (fail under 90%), CI Python coverage job, coverage in requirements-lint and .gitignore. Ci runs test-python-coverage.
- Raise c8 branches to 90%; add c8 ignore in heading-numbering for unreachable branch.
- Extend test_verify_markdownlint_fixtures tests (find_markdownlint_cmd, load_expected_errors, parse output, to_count_map, verify_file edge cases, main return/verbose). Add rule unit tests for edge cases and coverage paths.

Author: cypher0n3

.github/workflows/python-tests.yml

@@ -1,6 +1,7 @@
 name: Python tests
 
-# Unit tests for test-scripts/*.py (unittest). NOTE: Keep in sync with 'test-python' Makefile target.
+# Unit tests and coverage for test-scripts/*.py. Keep in sync with 'test-python' and
+# 'test-python-coverage' Makefile targets.
 
 on:
   push:
@@ -24,3 +25,21 @@ jobs:
 
       - name: Run Python unit tests
         run: make test-python
+
+  coverage:
+    name: Python coverage
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.11'
+
+      - name: Install coverage
+        run: pip install coverage
+
+      - name: Run Python coverage (fail if < 90%)
+        run: make test-python-coverage

.gitignore

@@ -37,6 +37,7 @@ tmp/
 
 # Ignore coverage files
 coverage.*
+.coverage
 
 # Ignore Python cache files
 **/__pycache__/

.markdownlint-rules/heading-numbering.js

@@ -53,9 +53,11 @@ function getSiblings(sorted, parentIndex, i) {
     if (parentIndex[j] !== parentIndex[i]) {
       continue;
     }
+    /* c8 ignore start -- same parent implies same level by tree construction */
     if (sorted[j].level !== h.level) {
       continue;
     }
+    /* c8 ignore stop */
     siblings.push({ index: j, ...sorted[j] });
   }
   siblings.sort((a, b) => a.lineNumber - b.lineNumber);
@@ -76,17 +78,21 @@ function getExpectedNumberInSection(sorted, parentIndex, i) {
 
   const siblings = getSiblings(sorted, parentIndex, i);
   const myIdx = siblings.findIndex((s) => s.lineNumber === h.lineNumber);
+  /* c8 ignore start -- current heading is always in its sibling list */
   if (myIdx < 0) {
     return null;
   }
+  /* c8 ignore stop */
 
   const firstNumbered = siblings.find((s) =>
     parseHeadingNumberPrefix(s.rawText).numbering != null
   );
+  /* c8 ignore start -- sectionUsesNum ensures at least one numbered sibling */
   const firstNumbering =
     firstNumbered != null
       ? parseHeadingNumberPrefix(firstNumbered.rawText).numbering
       : null;
+  /* c8 ignore stop */
   const startAtZero = firstNumbering === "0";
   const nextNum = startAtZero ? myIdx : myIdx + 1;
   const prefix = parentNum ? parentNum + "." : "";
@@ -111,9 +117,11 @@ function getSectionPeriodStyle(sorted, parentIndex, i) {
   const firstNumbered = siblings.find((s) =>
     parseHeadingNumberPrefix(s.rawText).numbering != null
   );
+  /* c8 ignore start -- getPeriodStyleError only called for numbered headings */
   if (firstNumbered == null) {
     return null;
   }
+  /* c8 ignore stop */
   return parseHeadingNumberPrefix(firstNumbered.rawText).hasH2Dot;
 }
 

Makefile

@@ -1,7 +1,7 @@
-.PHONY: ci lint-js lint-readmes lint-python test-markdownlint test-python test-rules test-rules-coverage venv
+.PHONY: ci lint-js lint-readmes lint-python test-markdownlint test-python test-python-coverage test-rules test-rules-coverage venv
 
 # Run all CI checks (same as GitHub Actions workflows). Run after 'npm install' and optionally 'make venv'.
-ci: lint-js test-rules-coverage test-markdownlint lint-python test-python lint-readmes
+ci: lint-js test-rules-coverage test-markdownlint lint-python test-python-coverage test-python lint-readmes
 
 # README linting - performs same checks as GitHub Actions workflow
 # NOTE: This target must be kept in sync with .github/workflows/lint-readmes.yml.
@@ -158,6 +158,21 @@ test-python:
 	}
 	@python3 -m unittest discover -s test-scripts -p "test_*.py" -v
 
+# Python unit test coverage - runs tests with coverage, fails if coverage < 90%.
+# Requires: pip install coverage (or make venv). Sources: test-scripts/*.py (excl. test_*.py).
+test-python-coverage:
+	@command -v python3 >/dev/null 2>&1 || { \
+		echo "Error: python3 not found. Install Python 3 to run coverage."; \
+		exit 1; \
+	}
+	@command -v coverage >/dev/null 2>&1 || [ -x .venv/bin/coverage ] || { \
+		echo "Error: coverage not found. Install with: pip install coverage or run 'make venv'"; \
+		exit 1; \
+	}
+	@if [ -d .venv ]; then PATH="$(CURDIR)/.venv/bin:$$PATH"; export PATH; fi; \
+	coverage run -m unittest discover -s test-scripts -p "test_*.py" && \
+	coverage report --include="test-scripts/*.py" --omit="test-scripts/test_*.py" --fail-under=90
+
 # Python venv for lint tooling - creates .venv and installs test-scripts/requirements-lint.txt
 # Run once (or after adding/updating test-scripts/requirements-lint.txt) so make lint-python uses the venv.
 # Usage: make venv