task: add tests for task::Builder::spawn_local (#7697)

tokio/src/task/builder.rs

@@ -118,20 +118,23 @@ impl<'a> Builder<'a> {
         })
     }
 
-    /// Spawns `!Send` a task on the current [`LocalSet`] with this builder's
-    /// settings.
+    /// Spawns `!Send` a task on the current [`LocalSet`] or [`LocalRuntime`] with
+    /// this builder's settings.
     ///
     /// The spawned future will be run on the same thread that called `spawn_local`.
-    /// This may only be called from the context of a [local task set][`LocalSet`].
+    /// This may only be called from the context of a [local task set][`LocalSet`]
+    /// or a [`LocalRuntime`].
     ///
     /// # Panics
     ///
-    /// This function panics if called outside of a [local task set][`LocalSet`].
+    /// This function panics if called outside of a [local task set][`LocalSet`]
+    /// or a [`LocalRuntime`].
     ///
     /// See [`task::spawn_local`] for more details.
     ///
     /// [`task::spawn_local`]: crate::task::spawn_local
     /// [`LocalSet`]: crate::task::LocalSet
+    /// [`LocalRuntime`]: crate::runtime::LocalRuntime
     #[track_caller]
     pub fn spawn_local<Fut>(self, future: Fut) -> io::Result<JoinHandle<Fut::Output>>
     where

tokio/src/task/join_set.rs

@@ -177,7 +177,7 @@ impl<T: 'static> JoinSet<T> {
     ///
     /// # Panics
     ///
-    /// This method panics if it is called outside of a `LocalSet`or `LocalRuntime`.
+    /// This method panics if it is called outside of a `LocalSet` or `LocalRuntime`.
     ///
     /// [`LocalSet`]: crate::task::LocalSet
     /// [`LocalRuntime`]: crate::runtime::LocalRuntime
@@ -748,8 +748,8 @@ impl<'a, T: 'static> Builder<'a, T> {
             .insert(self.builder.spawn_blocking_on(f, handle)?))
     }
 
-    /// Spawn the provided task on the current [`LocalSet`] with this builder's
-    /// settings, and store it in the [`JoinSet`].
+    /// Spawn the provided task on the current [`LocalSet`] or [`LocalRuntime`]
+    /// with this builder's settings, and store it in the [`JoinSet`].
     ///
     /// # Returns
     ///
@@ -757,9 +757,10 @@ impl<'a, T: 'static> Builder<'a, T> {
     ///
     /// # Panics
     ///
-    /// This method panics if it is called outside of a `LocalSet`.
+    /// This method panics if it is called outside of a `LocalSet` or `LocalRuntime`.
     ///
     /// [`LocalSet`]: crate::task::LocalSet
+    /// [`LocalRuntime`]: crate::runtime::LocalRuntime
     /// [`AbortHandle`]: crate::task::AbortHandle
     #[track_caller]
     pub fn spawn_local<F>(self, future: F) -> std::io::Result<AbortHandle>

tokio/tests/task_builder.rs

@@ -14,6 +14,34 @@ async fn spawn_with_name() {
     assert_eq!(result.unwrap(), "task executed");
 }
 
+#[tokio::test(flavor = "local")]
+async fn spawn_local_on_local_runtime() {
+    let result = Builder::new()
+        .spawn_local(async { "task executed" })
+        .unwrap()
+        .await;
+
+    assert_eq!(result.unwrap(), "task executed");
+}
+
+#[tokio::test]
+#[should_panic = "`spawn_local` called from outside of a `task::LocalSet` or `runtime::LocalRuntime`"]
+async fn spawn_local_panics_outside_local_set_or_local_runtime() {
+    let _ = Builder::new()
+        .spawn_local(async { "task executed" })
+        .unwrap()
+        .await;
+}
+
+#[tokio::test(flavor = "multi_thread")]
+#[should_panic = "`spawn_local` called from outside of a `task::LocalSet` or `runtime::LocalRuntime`"]
+async fn spawn_local_panics_in_multi_thread_runtime() {
+    let _ = Builder::new()
+        .spawn_local(async { "task executed" })
+        .unwrap()
+        .await;
+}
+
 #[tokio::test]
 async fn spawn_blocking_with_name() {
     let result = Builder::new()