headless-safe filedialog tests with optional live dialog tests and ruff fixes

test/conftest.py

@@ -0,0 +1,31 @@
+"""Make the test suite runnable on machines without Tk system libraries.
+
+``utils.filedialogs`` imports tkinter at module level, and the CI runner
+lacks the Tk shared libraries (``import tkinter`` fails on a missing
+``libtk8.6.so``). Since pytest imports every test module at collection
+time — including the deselected ``test_filedialogs_live.py`` — a minimal
+stub is registered in ``sys.modules`` here, before any test module is
+imported, whenever tkinter is not importable.
+
+The hermetic tests in ``test_filedialogs.py`` mock every tkinter
+touchpoint anyway, so the stub is never actually used.
+"""
+
+import sys
+import types
+
+try:
+    import tkinter  # noqa: F401
+except ImportError:
+    _tk_stub = types.ModuleType("tkinter")
+    _filedialog_stub = types.ModuleType("tkinter.filedialog")
+
+    def _tk_unavailable(*args, **kwargs):
+        raise AssertionError("real tkinter was called without a display")
+
+    _tk_stub.Tk = _tk_unavailable
+    _tk_stub.filedialog = _filedialog_stub
+    _filedialog_stub.askdirectory = _tk_unavailable
+    _filedialog_stub.askopenfilename = _tk_unavailable
+    sys.modules["tkinter"] = _tk_stub
+    sys.modules["tkinter.filedialog"] = _filedialog_stub