MIL-008: Choose level

Review record RC-041 (Go, autonomous mode, not independent).

Task: MIL-008#1
Task: MIL-008#2
Task: MIL-008#3
Task: MIL-008#4
Task: MIL-008#5
Task: MIL-008#6
Task: MIL-008#7
Task: MIL-008#8

tests/e2e/conftest.py

@@ -0,0 +1,22 @@
+"""Fixtures shared by the end-to-end tests."""
+
+import tkinter as tk
+from collections.abc import Iterator
+
+import pytest
+
+
+@pytest.fixture(scope="session")
+def tk_root() -> Iterator[tk.Tk]:
+    """The one Tk root of the process, shared by every e2e module.
+
+    A second interpreter right after destroying the first fails to find
+    init.tcl on some Windows Python installs, so there is only one. Each test
+    builds its views on it and destroys their widgets afterwards.
+    """
+    try:
+        root = tk.Tk()
+    except tk.TclError:
+        pytest.skip("no display available for Tk")
+    yield root
+    root.destroy()