add a test for the memo hook

packages/hooks/tests/memo.rs

@@ -0,0 +1,73 @@
+#[tokio::test]
+async fn memo_updates() {
+    use std::cell::RefCell;
+
+    use dioxus::prelude::*;
+
+    thread_local! {
+        static VEC_SIGNAL: RefCell<Option<Signal<Vec<usize>, SyncStorage>>> = RefCell::new(None);
+    }
+
+    fn app() -> Element {
+        let mut vec = use_signal_sync(|| vec![0, 1, 2]);
+
+        // Signals should update if they are changed from another thread
+        use_hook(|| {
+            VEC_SIGNAL.with(|cell| {
+                *cell.borrow_mut() = Some(vec);
+            });
+            std::thread::spawn(move || {
+                std::thread::sleep(std::time::Duration::from_millis(100));
+                vec.push(5);
+            });
+        });
+
+        let len = vec.len();
+        let len_memo = use_memo(move || vec.len());
+
+        // Make sure memos that update in the middle of a component work
+        if generation() < 2 {
+            vec.push(len);
+        }
+        // The memo should always be up to date
+        assert_eq!(vec.len(), len_memo());
+
+        rsx! {
+            for i in 0..len {
+                Child {
+                    index: i,
+                    vec,
+                }
+            }
+        }
+    }
+
+    #[component]
+    fn Child(index: usize, vec: Signal<Vec<usize>, SyncStorage>) -> Element {
+        // This memo should not rerun after the element is removed
+        let item = use_memo(move || vec.read()[index]);
+
+        rsx! {
+            div { "Item: {item}" }
+        }
+    }
+
+    let mut dom = VirtualDom::new(app);
+
+    dom.rebuild_in_place();
+    let mut signal = VEC_SIGNAL.with(|cell| (*cell.borrow()).unwrap());
+    // Wait for the signal to update
+    for _ in 0..3 {
+        dom.wait_for_work().await;
+        dom.render_immediate(&mut dioxus::dioxus_core::NoOpMutations);
+        println!("Signal: {signal:?}");
+    }
+    assert_eq!(signal(), vec![0, 1, 2, 3, 4, 5]);
+    // Remove each element from the vec
+    for _ in 0..6 {
+        signal.pop();
+        dom.wait_for_work().await;
+        dom.render_immediate(&mut dioxus::dioxus_core::NoOpMutations);
+        println!("Signal: {signal:?}");
+    }
+}