refactor(workspace): enforce layered crate boundaries

crates/aether-testing/testkit/src/wait.rs

@@ -0,0 +1,50 @@
+use std::future::Future;
+use std::time::Duration;
+
+pub async fn wait_until<F, Fut>(
+    timeout: Duration,
+    poll_interval: Duration,
+    mut predicate: F,
+) -> bool
+where
+    F: FnMut() -> Fut,
+    Fut: Future<Output = bool>,
+{
+    let deadline = tokio::time::Instant::now() + timeout;
+    loop {
+        if predicate().await {
+            return true;
+        }
+        if tokio::time::Instant::now() >= deadline {
+            return false;
+        }
+        tokio::time::sleep(poll_interval).await;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    use std::sync::Arc;
+    use std::time::Duration;
+
+    use super::wait_until;
+
+    #[tokio::test]
+    async fn returns_true_when_predicate_eventually_passes() {
+        let flag = Arc::new(AtomicBool::new(false));
+        let background = flag.clone();
+        tokio::spawn(async move {
+            tokio::time::sleep(Duration::from_millis(10)).await;
+            background.store(true, Ordering::Release);
+        });
+
+        let ready = wait_until(Duration::from_millis(100), Duration::from_millis(5), || {
+            let flag = flag.clone();
+            async move { flag.load(Ordering::Acquire) }
+        })
+        .await;
+
+        assert!(ready);
+    }
+}