add toast and alert overlays to the shell

crates/layout/tests/shell.rs

@@ -235,3 +235,88 @@ fn the_right_seam_grows_the_right_sidebar_leftwards() {
     let region = bounds(&mut visual, "test-right").expect("right region missing");
     assert_eq!(region.size.width, grown);
 }
+
+/// Toasts and alerts live on the shell's [`LayoutState`]; pushing one must
+/// show up in the rendered shell with no observing or manual overlay.
+#[cfg(feature = "toast")]
+mod toasts {
+    use super::*;
+    use gpui_native_core::toast::{Toast, ToastAction};
+    use std::time::Duration;
+
+    #[test]
+    fn a_pushed_toast_renders_in_the_shell() {
+        let mut cx = TestAppContext::single();
+        let (state, mut visual) = layout_window(&mut cx);
+
+        let id = cx.update(|cx| {
+            state.update(cx, |state, cx| {
+                state.push_toast(
+                    Toast::new("Draft deleted").action(ToastAction::new("Undo", |_| {
+                        // A real app restores the draft here.
+                    })),
+                    cx,
+                )
+            })
+        });
+        // No redraw, no observation: the shell repaints its own overlay.
+        cx.run_until_parked();
+        assert!(
+            bounds(&mut visual, "toast-pill").is_some(),
+            "the pushed toast must appear in the shell's overlay"
+        );
+
+        cx.update(|cx| {
+            state.update(cx, |state, cx| state.dismiss_toast(id, cx));
+        });
+        cx.run_until_parked();
+        // The fade-out keeps the pill mounted briefly.
+        assert!(
+            bounds(&mut visual, "toast-pill").is_some(),
+            "the dismissed toast must stay mounted through its fade-out"
+        );
+        cx.executor().advance_clock(Duration::from_secs(2));
+        cx.run_until_parked();
+        assert!(
+            bounds(&mut visual, "toast-pill").is_none(),
+            "the dismissed toast must leave the overlay once faded"
+        );
+    }
+}
+
+#[cfg(feature = "alert")]
+mod alerts {
+    use super::*;
+    use gpui_native_core::alert::{Alert, AlertSeverity};
+
+    #[test]
+    fn a_pushed_alert_renders_in_the_shell() {
+        let mut cx = TestAppContext::single();
+        let (state, mut visual) = layout_window(&mut cx);
+
+        cx.update(|cx| {
+            state.update(cx, |state, cx| {
+                state.push_alert(
+                    Alert::new("shell-alert")
+                        .title("Backed up")
+                        .severity(AlertSeverity::Info),
+                    cx,
+                );
+            })
+        });
+        cx.run_until_parked();
+        assert!(
+            bounds(&mut visual, "alert-entry").is_some(),
+            "the pushed alert must appear in the shell's overlay"
+        );
+
+        cx.update(|cx| {
+            state.update(cx, |state, cx| state.clear_alerts(cx));
+        });
+        cx.run_until_parked();
+        assert!(
+            bounds(&mut visual, "alert-entry").is_none(),
+            "cleared alerts must leave the overlay"
+        );
+    }
+}