[wic][PATCH v2 4/9] tests: add optional coverage reporting to run-tests.sh

Knowing which lines a test run actually exercised is the difference
between "the suite is green" and "the suite is green and we know what
it touched". This commit wires branch coverage of the wic source into
the runner, kept entirely opt-in so a plain run stays fast and quiet.

pyproject.toml gains coverage and pytest-cov in the tests extra, so
"pip install -e .[tests]" pulls in what the new flags need.

run-tests.sh gains two options:

  - --coverage measures branch coverage of src/wic during the run and
    prints a terminal report listing the lines that were missed;

  - --html [DIR] additionally writes a browsable HTML report (default
    htmlcov/, or DIR if given) and implies --coverage.

If --coverage is requested but pytest-cov is not installed the runner
fails loudly with the install command rather than running without the
measurement it was asked for.

The coverage data file and the HTML report directory are build
artifacts, so .gitignore learns to ignore .coverage and htmlcov/.

AI-Generated: codex/claude-opus 4.7 (xhigh)
Signed-off-by: Trevor Woerner <[email protected]>
---
changes in v2:
- v1 submitted the entire test suite as a single commit; v2 breaks
  the work into a reviewable series, and this patch is one step of it.
---
 .gitignore         |  4 ++++
 pyproject.toml     |  2 ++
 tests/run-tests.sh | 39 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index 07992096c0fb..534c49538091 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,7 @@
 
 # pytest cache
 /.pytest_cache/
+
+# coverage data and reports
+/.coverage
+/htmlcov/
diff --git a/pyproject.toml b/pyproject.toml
index d660e39007c4..ece2757bb686 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,6 +24,8 @@ Repository = "https://git.yoctoproject.org/wic"
 [project.optional-dependencies]
 tests = [
     "pytest >= 7.0",
+    "coverage >= 7.0",
+    "pytest-cov >= 4.0",
 ]
 
 [project.scripts]
diff --git a/tests/run-tests.sh b/tests/run-tests.sh
index 9db6d50338d6..a483da6a63a6 100755
--- a/tests/run-tests.sh
+++ b/tests/run-tests.sh
@@ -13,9 +13,13 @@ set -euo pipefail
 usage() {
     cat <<'USAGE'
 Usage:
-  tests/run-tests.sh [pytest args]
+  tests/run-tests.sh [--coverage] [--html [DIR]] [pytest args]
 
 Options:
+  --coverage    also measure branch coverage of src/wic and print a
+                terminal report listing the lines that were missed
+  --html [DIR]  also write an HTML coverage report (default dir:
+                htmlcov/); implies --coverage
   -h, --help    show this help and exit
 
 Anything else is passed straight through to pytest (for example a
@@ -24,6 +28,9 @@ tests/ is run.
 
 Examples:
   tests/run-tests.sh                  # whole suite
+  tests/run-tests.sh --coverage       # + terminal coverage report
+  tests/run-tests.sh --html           # + HTML report in htmlcov/
+  tests/run-tests.sh --html /tmp/cov  # + HTML report in /tmp/cov
   tests/run-tests.sh -k filemap -v    # pass args through to pytest
   tests/run-tests.sh tests/unit       # a single tier or file
 
@@ -34,9 +41,25 @@ USAGE
 REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 PY="${PYTHON:-python3}"
 
+coverage=0
+html=0
+html_dir="htmlcov"
 pytest_args=()
 while [ $# -gt 0 ]; do
     case "$1" in
+        --coverage)
+            coverage=1
+            ;;
+        --html)
+            coverage=1
+            html=1
+            # Optional directory argument: consume the next token only if
+            # it is not another option or the pytest pass-through marker.
+            case "${2:-}" in
+                ""|-*|--) ;;
+                *) html_dir="$2"; shift ;;
+            esac
+            ;;
         -h|--help)
             usage
             exit 0
@@ -72,4 +95,18 @@ if [ ${#pytest_args[@]} -eq 0 ]; then
     pytest_args=("tests")
 fi
 
+if [ "$coverage" -eq 1 ]; then
+    if ! "$PY" -c "import pytest_cov" >/dev/null 2>&1; then
+        echo "error: coverage requested but pytest-cov is not installed." >&2
+        echo "       run: $PY -m pip install -e \".[tests]\"" >&2
+        exit 1
+    fi
+    cov_args=(--cov=wic --cov-branch --cov-report=term-missing)
+    if [ "$html" -eq 1 ]; then
+        cov_args+=(--cov-report="html:${html_dir}")
+        echo "HTML coverage report: ${html_dir}/index.html" >&2
+    fi
+    exec "$PY" -m pytest "${pytest_args[@]}" "${cov_args[@]}"
+fi
+
 exec "$PY" -m pytest "${pytest_args[@]}"
-- 
2.50.0.173.g8b6f19ccfc3a