msglist test [nfc]: Pull out getAnimation helper

Author: sirpengi

test/widgets/message_list_test.dart

@@ -302,9 +302,9 @@ void main() {
   });
 
   group('_UnreadMarker animations', () {
-    Animation getAnimation(WidgetTester tester) {
+    Animation getAnimation(WidgetTester tester, int messageId) {
       final widget = tester.widget<FadeTransition>(find.descendant(
-        of: find.byType(MessageItem),
+        of: find.byKey(ValueKey(messageId)),
         matching: find.byType(FadeTransition)));
       return widget.opacity;
     }
@@ -313,23 +313,23 @@ void main() {
       final message = eg.streamMessage(flags: [MessageFlag.read]);
       await setupMessageListPage(tester, messages: [message]);
 
-      check(getAnimation(tester).value).equals(0);
+      check(getAnimation(tester, message.id).value).equals(0);
 
       store.handleEvent(eg.updateMessageFlagsRemoveEvent(
         MessageFlag.read, [message]));
       await tester.pump(); // process handleEvent
-      check(getAnimation(tester).status).equals(AnimationStatus.forward);
+      check(getAnimation(tester, message.id).status).equals(AnimationStatus.forward);
 
       await tester.pumpAndSettle();
 
-      check(getAnimation(tester).value).equals(1.0);
+      check(getAnimation(tester, message.id).value).equals(1.0);
     });
 
     testWidgets('from unread to read', (WidgetTester tester) async {
       final message = eg.streamMessage(flags: []);
       await setupMessageListPage(tester, messages: [message]);
 
-      check(getAnimation(tester).value).equals(1.0);
+      check(getAnimation(tester, message.id).value).equals(1.0);
 
       store.handleEvent(UpdateMessageFlagsAddEvent(
         id: 1,
@@ -338,25 +338,16 @@ void main() {
         all: false,
       ));
       await tester.pump(); // process handleEvent
-      check(getAnimation(tester).status).equals(AnimationStatus.forward);
+      check(getAnimation(tester, message.id).status).equals(AnimationStatus.forward);
 
       await tester.pumpAndSettle();
 
-      check(getAnimation(tester).value).equals(0);
+      check(getAnimation(tester, message.id).value).equals(0);
     });
 
     testWidgets('animation state persistence', (WidgetTester tester) async {
       // Check that _UnreadMarker maintains its in-progress animation
       // as the number of items change in MessageList.
-
-      // TODO: pull this out into group
-      Animation getAnimation(WidgetTester tester, int messageId) {
-        final widget = tester.widget<FadeTransition>(find.descendant(
-          of: find.byKey(ValueKey(messageId)),
-          matching: find.byType(FadeTransition)));
-        return widget.opacity;
-      }
-
       final message = eg.streamMessage(flags: []);
       await setupMessageListPage(tester, messages: [message]);