Keymap discovery runs its fresh-interpreter case in a new interpreter

tests/support/keymap_discovery.py

@@ -0,0 +1,19 @@
+"""Run as its own interpreter: keymap discovery imports a screen nothing in it has opened.
+
+tests/textual/test_keymap_discovery.py starts it with `python -m`, because the app test
+template imports every toad module before it forks a test.
+"""
+
+import sys
+
+from toad.key_modes import KeyMode, Standard
+from toad.keymap import KeymapCatalog, KeymapRow
+
+assert "toad.screens.welcome" not in sys.modules
+catalog = KeymapCatalog.capture(tuple(KeyMode.members_with(KeyMode)))
+assert "toad.screens.welcome" in sys.modules
+from toad.screens.welcome import NewSessionAction  # noqa: E402 - discovery imported it
+
+row = KeymapRow.of(NewSessionAction(), Standard)
+assert catalog.require(row.declaration).key_title() == NewSessionAction().key_title()
+assert catalog.defaults(row) == NewSessionAction.keys[Standard.binding_mode()]

tests/textual/test_keymap_discovery.py

@@ -1,18 +1,15 @@
 """Discovery includes screens that the current application has not opened."""
 
+from pathlib import Path
+import subprocess
 import sys
 
-from toad.key_modes import KeyMode, Standard
-from toad.keymap import KeymapCatalog, KeymapRow
+TESTS = Path(__file__).resolve().parents[1]
 
 
 def test_unopened_screen_invocations_are_discovered_in_a_fresh_process(workspace):
-    # `workspace` gives this case its own interpreter, independent of other imports.
-    assert "toad.screens.welcome" not in sys.modules
-    catalog = KeymapCatalog.capture(tuple(KeyMode.members_with(KeyMode)))
-    assert "toad.screens.welcome" in sys.modules
-    from toad.screens.welcome import NewSessionAction
-
-    row = KeymapRow.of(NewSessionAction(), Standard)
-    assert catalog.require(row.declaration).key_title() == NewSessionAction().key_title()
-    assert catalog.defaults(row) == NewSessionAction.keys[Standard.binding_mode()]
+    # The app test template imports every toad module before it forks, so only a new
+    # interpreter starts without the welcome screen; `workspace` gives it this case's roots.
+    run = subprocess.run([sys.executable, "-m", "support.keymap_discovery"],
+                         cwd=TESTS, capture_output=True, text=True, timeout=60)
+    assert run.returncode == 0, run.stderr