Add unit test for ChildView

crates/gpui/src/app.rs

@@ -7044,4 +7044,73 @@ mod tests {
         cx.simulate_window_activation(Some(window_3));
         assert_eq!(mem::take(&mut *events.borrow_mut()), []);
     }
+
+    #[crate::test(self)]
+    fn test_child_view(cx: &mut MutableAppContext) {
+        struct Child {
+            rendered: Rc<Cell<bool>>,
+            dropped: Rc<Cell<bool>>,
+        }
+
+        impl super::Entity for Child {
+            type Event = ();
+        }
+
+        impl super::View for Child {
+            fn ui_name() -> &'static str {
+                "child view"
+            }
+
+            fn render(&mut self, _: &mut RenderContext<Self>) -> ElementBox {
+                self.rendered.set(true);
+                Empty::new().boxed()
+            }
+        }
+
+        impl Drop for Child {
+            fn drop(&mut self) {
+                self.dropped.set(true);
+            }
+        }
+
+        struct Parent {
+            child: Option<ViewHandle<Child>>,
+        }
+
+        impl super::Entity for Parent {
+            type Event = ();
+        }
+
+        impl super::View for Parent {
+            fn ui_name() -> &'static str {
+                "parent view"
+            }
+
+            fn render(&mut self, cx: &mut RenderContext<Self>) -> ElementBox {
+                if let Some(child) = self.child.as_ref() {
+                    ChildView::new(child, cx).boxed()
+                } else {
+                    Empty::new().boxed()
+                }
+            }
+        }
+
+        let child_rendered = Rc::new(Cell::new(false));
+        let child_dropped = Rc::new(Cell::new(false));
+        let (_, root_view) = cx.add_window(Default::default(), |cx| Parent {
+            child: Some(cx.add_view(|_| Child {
+                rendered: child_rendered.clone(),
+                dropped: child_dropped.clone(),
+            })),
+        });
+        assert!(child_rendered.take());
+        assert!(!child_dropped.take());
+
+        root_view.update(cx, |view, cx| {
+            view.child.take();
+            cx.notify();
+        });
+        assert!(!child_rendered.take());
+        assert!(child_dropped.take());
+    }
 }