added test

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - `TextArea.line_number_start` reactive attribute https://github.com/Textualize/textual/pull/4471
+- Added `DOMNode.mutate_reactive`
 
 ### Fixed
 

src/textual/reactive.py

@@ -287,7 +287,7 @@ def _set(self, obj: Reactable, value: ReactiveType, always: bool = False) -> Non
         if callable(public_validate_function):
             value = public_validate_function(value)
         # If the value has changed, or this is the first time setting the value
-        if always or current_value != value or self._always_update:
+        if always or self._always_update or current_value != value:
             # Store the internal value
             setattr(obj, self.internal_name, value)
 

tests/test_reactive.py

@@ -735,7 +735,6 @@ def on_test_widget_test_message(self, event: TestWidget.TestMessage) -> None:
             message_senders.append(event._sender)
 
     class TestApp(App[None]):
-
         def compose(self) -> ComposeResult:
             yield TestContainer()
 
@@ -744,3 +743,43 @@ def compose(self) -> ComposeResult:
         pilot.app.query_one(TestWidget).make_reaction()
         await pilot.pause()
         assert message_senders == [pilot.app.query_one(TestWidget)]
+
+
+async def test_mutate_reactive() -> None:
+    """Test explicitly mutating reactives"""
+
+    watched_names: list[list[str]] = []
+
+    class TestWidget(Widget):
+        names: reactive[list[str]] = reactive(list)
+
+        def watch_names(self, names: list[str]) -> None:
+            watched_names.append(names.copy())
+
+    class TestApp(App):
+        def compose(self) -> ComposeResult:
+            yield TestWidget()
+
+    app = TestApp()
+    async with app.run_test():
+        widget = app.query_one(TestWidget)
+        # watch method called on startup
+        assert watched_names == [[]]
+
+        # Mutate the list
+        widget.names.append("Paul")
+        # No changes expected
+        assert watched_names == [[]]
+        # Explicitly mutate the reactive
+        widget.mutate_reactive(TestWidget.names)
+        # Watcher will be invoked
+        assert watched_names == [[], ["Paul"]]
+        # Make further modifications
+        widget.names.append("Jessica")
+        widget.names.remove("Paul")
+        # No change expected
+        assert watched_names == [[], ["Paul"]]
+        # Explicit mutation
+        widget.mutate_reactive(TestWidget.names)
+        # Watcher should be invoked
+        assert watched_names == [[], ["Paul"], ["Jessica"]]