added preflight check

tests/test_harness_guards.py

@@ -0,0 +1,116 @@
+"""Guards for the pytest harness itself.
+
+``tests/conftest.py`` was accidentally deleted in commit edc6e42 while four test
+modules still depended on its fixtures, which made the suite unrunnable without
+anything failing loudly in CI. These tests turn that class of regression into an
+explicit failure, and also catch a stale ``orisys`` install silently shadowing
+``src/orisys`` (a real hazard: base/py312 environments have older orisys copies
+in site-packages).
+"""
+
+from __future__ import annotations
+
+import functools
+import importlib.util
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+CONFTEST_PATH = Path(__file__).resolve().parent / "conftest.py"
+
+# Names that must exist in tests/conftest.py.
+REQUIRED_CONFTEST_NAMES = (
+    "DEFAULT_VIDEO_CANDIDATES",
+    "make_sensor",
+    "test_video_path",
+    "test_config_name",
+    "available_backends",
+    "sensor_factory",
+)
+
+# Fixtures that must be resolvable through pytest.
+REQUIRED_FIXTURES = (
+    "test_video_path",
+    "test_config_name",
+    "available_backends",
+    "sensor_factory",
+)
+
+
+@functools.lru_cache(maxsize=1)
+def _load_conftest_module():
+    """Load tests/conftest.py by path so a deletion is observable here."""
+    spec = importlib.util.spec_from_file_location("_orisys_conftest_probe", CONFTEST_PATH)
+    if spec is None or spec.loader is None:
+        raise AssertionError(f"Cannot load {CONFTEST_PATH}")
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_conftest_defines_shared_fixtures():
+    assert CONFTEST_PATH.is_file(), (
+        f"{CONFTEST_PATH} is missing. test_backends.py, test_smoke_api.py, "
+        "test_errors_and_cleanup.py and test_longrun_stability.py depend on its "
+        "fixtures; it was accidentally deleted in commit edc6e42. Restore it "
+        "instead of deleting it."
+    )
+
+    module = _load_conftest_module()
+    missing = [
+        name for name in REQUIRED_CONFTEST_NAMES if getattr(module, name, None) is None
+    ]
+    assert not missing, (
+        f"tests/conftest.py no longer defines: {', '.join(missing)}. "
+        "The shared sensor-test fixtures are required by the suite."
+    )
+
+
+def test_default_test_video_is_reachable():
+    """At least one default candidate must exist, or every sensor test skips."""
+    module = _load_conftest_module()
+    candidates = [REPO_ROOT / Path(rel) for rel in module.DEFAULT_VIDEO_CANDIDATES]
+    existing = [path for path in candidates if path.is_file()]
+    assert existing, (
+        "None of the default test videos exist:\n  "
+        + "\n  ".join(str(path) for path in candidates)
+        + "\nCommit a sample clip under data/sample/ or set ORISYS_TEST_VIDEO."
+    )
+
+
+def test_fixtures_are_registered_with_pytest(request):
+    missing: list[str] = []
+    for name in REQUIRED_FIXTURES:
+        try:
+            request.getfixturevalue(name)
+        except pytest.FixtureLookupError:
+            missing.append(name)
+    assert not missing, (
+        f"pytest did not register these fixtures: {', '.join(missing)}. "
+        "Check that tests/conftest.py is present and the @pytest.fixture "
+        "decorators are intact."
+    )
+
+
+def test_tests_run_against_checkout_not_stale_install():
+    """Fail loudly when an old orisys in site-packages shadows src/orisys."""
+    src_pkg = (REPO_ROOT / "src" / "orisys").resolve()
+    if not src_pkg.is_dir():
+        pytest.skip("src/orisys is not present in this checkout layout")
+
+    import orisys
+
+    module_file = getattr(orisys, "__file__", None)
+    assert module_file, (
+        "import orisys resolved to a namespace package (__file__ is None) "
+        f"instead of {src_pkg}. A stale orisys in site-packages is shadowing "
+        "the checkout; run `pip uninstall -y orisys` in this environment."
+    )
+
+    resolved_parent = Path(module_file).resolve().parent
+    assert resolved_parent == src_pkg, (
+        f"import orisys resolved to {resolved_parent} instead of {src_pkg}. "
+        "A stale orisys in site-packages is shadowing the checkout; run "
+        "`pip uninstall -y orisys` in this environment."
+    )