Only mount if container is mounted

Textualize/textual#4570

tests/test_app.py

@@ -175,19 +175,19 @@ async def test_image_step(example_code, image_path: Path):
     async with app.run_test() as pilot:
         # Initial state should be ImageStep
         assert isinstance(app.current_chapter.current_step, ImageStep)
-        assert app.current_chapter.image_display.visible
+        assert app.current_chapter.image_container.visible
         assert not app.current_chapter.code_display.visible
 
         # Move to next step (Code Step)
         await pilot.press("down")
         assert isinstance(app.current_chapter.current_step, Step)
-        assert not app.current_chapter.image_display.visible
+        assert not app.current_chapter.image_container.visible
         assert app.current_chapter.code_display.visible
 
         # Move back to ImageStep
         await pilot.press("up")
         assert isinstance(app.current_chapter.current_step, ImageStep)
-        assert app.current_chapter.image_display.visible
+        assert app.current_chapter.image_container.visible
         assert not app.current_chapter.code_display.visible
 
 
@@ -203,12 +203,12 @@ async def test_toggle_dim_image_step(example_code, image_path: Path):
 
     async with app.run_test() as pilot:
         # Initial state should be ImageStep
-        assert app.current_chapter.image_display.visible
+        assert app.current_chapter.image_container.visible
         assert not app.current_chapter.code_display.visible
 
         # Press toggle_dim key
         await pilot.press("d")
 
         # Ensure toggle_dim didn't affect ImageStep and code display is still not visible
-        assert app.current_chapter.image_display.visible
+        assert app.current_chapter.image_container.visible
         assert not app.current_chapter.code_display.visible

tuitorial/app.py

@@ -69,7 +69,8 @@ def update_display(self) -> None:
             for widget in self.image_container.walk_children():
                 widget.remove()
             image_widget = Image(step.image_path)
-            self.image_container.mount(image_widget)
+            if self.image_container.is_mounted:
+                self.image_container.mount(image_widget)
 
         self.description.update(
             f"Step {self.current_index + 1}/{len(self.steps)}\n{step.description}",