Add regression test

envisage/ui/tasks/tests/test_preferences_pane.py

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+# (C) Copyright 2007-2023 Enthought, Inc., Austin, TX
+# All rights reserved.
+#
+# This software is provided without warranty under the terms of the BSD
+# license included in LICENSE.txt and may be redistributed only under
+# the conditions described in the aforementioned license. The license
+# is also available online at http://www.enthought.com/licenses/BSD.txt
+#
+# Thanks for using Enthought open source!
+
+"""Tests for the PreferencesPane."""
+
+
+import unittest
+
+
+from apptools.preferences.api import (
+    Preferences,
+    PreferencesHelper,
+    ScopedPreferences,
+)
+from traits.api import Str
+from traitsui.api import Item, View
+
+from envisage.ui.tasks.api import PreferencesPane
+
+
+class MyPreferences(PreferencesHelper):
+    #: The node that contains the preferences.
+    preferences_path = "app"
+
+    #: The user's favourite colour
+    color = Str()
+
+
+class MyPreferencesPane(PreferencesPane):
+
+    model_factory = MyPreferences
+
+    view = View(
+        Item("color"),
+    )
+
+
+class TestPreferencesPane(unittest.TestCase):
+    def test_no_preference_changes_without_apply(self):
+        # Regression test for https://github.com/enthought/envisage/issues/582
+        default_preferences = Preferences(name="default")
+        default_preferences.set("app.color", "red")
+
+        application_preferences = Preferences(name="application")
+        preferences = ScopedPreferences(
+            scopes=[application_preferences, default_preferences]
+        )
+
+        helper = MyPreferences(preferences=preferences)
+        self.assertIsNone(application_preferences.get("app.color"))
+        pane = MyPreferencesPane(model=helper)
+
+        object_context = pane.trait_context()["object"]
+
+        # At this point, the application preferences should still not
+        # have an app.color setting
+        self.assertIsNone(object_context.color)