enable python unit test (#15593)

* enable python unit test

* fix Windows

* Require numpy for the plugin tests in CI

scripts/run_unit_tests.sh

@@ -2,7 +2,8 @@
 
 # This file is made to support the unit tests workflow.
 # It should only require the directories build/tests, scripts/, and tests/ to function,
-# and cmake (with ctest) installed.
+# and cmake (with ctest) installed -- plus network access to PyPI whenever numpy has to
+# be installed into a freshly built test tree (see below).
 # (otherwise, update the workflow too, but try to avoid to keep things self-contained)
 #
 # Usage: run_unit_tests.sh [TEST_DIR] [BUILD_CONFIG]
@@ -18,6 +19,52 @@ cd "${ROOT_DIR}" || exit 1
 TEST_DIR="${1:-build/tests}"
 BUILD_CONFIG="${2:-}"
 
+# The slic3rutils plugin-host tests build numpy arrays through the CPython copied next
+# to the test binary (see tests/slic3rutils/CMakeLists.txt), which ships no numpy.
+# Install it with the uv staged beside that runtime -- the tool the app installs plugin
+# dependencies with -- straight into the interpreter's own site-packages: no pip needed
+# in the runtime, no PYTHONPATH. Re-checked every run because a rebuild of the test
+# target re-copies the runtime; needs network whenever it installs. Pinned so a numpy
+# release cannot change results on its own.
+NUMPY_VERSION="2.5.3"
+
+# Without numpy those tests assert the numpy-absent error path instead, so a local run
+# only warns. Under CI it fails the run, which would otherwise stay green while silently
+# dropping the array coverage. (The Flatpak leg runs this inside `flatpak build`, whose
+# minimal environment has no CI, and its offline build stages no uv, so numpy stays
+# best-effort there.)
+numpy_unavailable() {
+    if [ -n "${CI:-}" ]; then
+        echo "error: $1" >&2
+        exit 1
+    fi
+    echo "warning: $1; the numpy-backed binding tests will cover only the numpy-absent path."
+}
+
+has_pinned_numpy() {
+    "${python_exe}" -c "import sys, numpy; sys.exit(numpy.__version__ != '${NUMPY_VERSION}')" >/dev/null 2>&1
+}
+
+find_args=("${TEST_DIR}" \( -path '*/python/bin/python3' -o -path '*/python/python.exe' \))
+# Multi-config trees hold one copy per configuration; only bootstrap the one being run.
+[ -n "${BUILD_CONFIG}" ] && find_args+=(-path "*/${BUILD_CONFIG}/*")
+python_exe="$(find "${find_args[@]}" -print -quit 2>/dev/null)"
+
+if [ -z "${python_exe}" ]; then
+    numpy_unavailable "no bundled Python under ${TEST_DIR}"
+elif ! has_pinned_numpy; then
+    uv_exe="${python_exe%/python/*}/tools/uv/uv"
+    # Builds that bundle no uv (Windows arm64) fall back to one on PATH.
+    [ -x "${uv_exe}" ] || uv_exe="$(command -v uv)"
+    echo "Installing numpy ${NUMPY_VERSION} into the embedded test interpreter (${python_exe})..."
+    if [ -z "${uv_exe}" ]; then
+        numpy_unavailable "no uv staged beside the tests or on PATH"
+    elif ! "${uv_exe}" pip install --python "${python_exe}" --only-binary :all: "numpy==${NUMPY_VERSION}" \
+            || ! has_pinned_numpy; then
+        numpy_unavailable "could not install numpy ${NUMPY_VERSION} into ${python_exe}"
+    fi
+fi
+
 # Run the whole suite, excluding tests tagged [NotWorking] and tests labelled RequiresApp,
 # which run the built orca-slicer binary that this directory does not contain.
 # --no-tests=error fails the job if the filter matches nothing (instead of passing green).