Fix a synchronous event bug in futureStream.

pkg/scheduled_test/lib/src/utils.dart

Index: pkg/scheduled_test/lib/src/utils.dart
diff --git a/pkg/scheduled_test/lib/src/utils.dart b/pkg/scheduled_test/lib/src/utils.dart
index 9a940cca8dd65b6d4a3f2b8c7e118f17c961be6d..2b8b78ef9e9dfd98143cdaacb6e75f88117ac809 100644
--- a/pkg/scheduled_test/lib/src/utils.dart
+++ b/pkg/scheduled_test/lib/src/utils.dart
@@ -91,9 +91,10 @@ Stream futureStream(Future<Stream> future, {bool broadcast: false}) {
   var controller;
 
   future = future.catchError((e, stackTrace) {
-    if (controller == null) return;
-    controller.addError(e, stackTrace);
-    controller.close();
+    // Since [controller] is synchronous, it's likely that emitting an error
+    // will cause it to be cancelled before we call close.
+    if (controller != null) controller.addError(e, stackTrace);
+    if (controller != null) controller.close();
     controller = null;
   });