Correct testbed tests of app icons.

cocoa/tests_backend/app.py

@@ -91,6 +91,7 @@ class AppProbe(BaseProbe):
             assert mid_color in {
                 (130, 100, 57, 255),
                 (130, 109, 66, 255),
+                (138, 107, 64, 255),
                 (138, 108, 64, 255),
                 (149, 119, 73, 255),
             }

testbed/tests/app/test_app.py

@@ -600,6 +600,6 @@ async def test_app_icon(app, app_probe):
     app_probe.assert_app_icon("resources/alt-icon")
 
     # Reset the icon to the default
-    app.icon = None
+    app.icon = toga.Icon.APP_ICON
     await app_probe.redraw("Revert app icon to default")
     app_probe.assert_app_icon(None)

testbed/tests/test_icons.py

@@ -1,7 +1,5 @@
 import re
-import sys
 from importlib import import_module
-from pathlib import Path
 
 import pytest
 
@@ -27,14 +25,9 @@ async def test_icon(app):
     probe.assert_icon_content(probe.alternate_resource)
 
 
-@pytest.mark.skipif(
-    Path(sys.executable).stem.startswith("python"),
-    reason="Can't test app icon in a dev mode test",
-)
 async def test_app_icon(app):
     """The app icon can be obtained."""
-    icon = toga.Icon(None)
-    probe = icon_probe(app, icon)
+    probe = icon_probe(app, toga.Icon.APP_ICON)
     probe.assert_app_icon_content()