autocomplete_test [nfc]: Rename findNetworkImage to findAvatarImage

Renamed the method and changed the avatar
finder implementation to check for userId
instead of avatar image URL.

Author: fombalang

test/widgets/autocomplete_test.dart

@@ -9,6 +9,7 @@ import 'package:zulip/model/localizations.dart';
 import 'package:zulip/model/narrow.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/model/typing_status.dart';
+import 'package:zulip/widgets/content.dart';
 import 'package:zulip/widgets/message_list.dart';
 
 import '../api/fake_api.dart';
@@ -108,18 +109,13 @@ void main() {
 
   group('ComposeAutocomplete', () {
 
-    Finder findNetworkImage(String url) {
-      return find.byWidgetPredicate((widget) => switch(widget) {
-        Image(image: NetworkImage(url: var imageUrl)) when imageUrl == url
-          => true,
-        _ => false,
-      });
-    }
+    Finder findAvatarImage(int userId) =>
+      find.byWidgetPredicate((widget) => widget is AvatarImage && widget.userId == userId);
 
     void checkUserShown(User user, PerAccountStore store, {required bool expected}) {
       check(find.text(user.fullName).evaluate().length).equals(expected ? 1 : 0);
       final avatarFinder =
-        findNetworkImage(store.tryResolveUrl(user.avatarUrl!).toString());
+        findAvatarImage(user.userId);
       check(avatarFinder.evaluate().length).equals(expected ? 1 : 0);
     }