test store [nfc]: Support adding delay to loadPerAccount

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

test/model/test_store.dart

@@ -125,6 +125,7 @@ class TestGlobalStore extends GlobalStore {
   }
 
   static const Duration removeAccountDuration = Duration(milliseconds: 1);
+  Duration? loadPerAccountDuration;
 
   /// Consume the log of calls made to [doRemoveAccount].
   List<int> takeDoRemoveAccountCalls() {
@@ -142,7 +143,10 @@ class TestGlobalStore extends GlobalStore {
   }
 
   @override
-  Future<PerAccountStore> doLoadPerAccount(int accountId) {
+  Future<PerAccountStore> doLoadPerAccount(int accountId) async {
+    if (loadPerAccountDuration != null) {
+      await Future<void>.delayed(loadPerAccountDuration!);
+    }
     final initialSnapshot = _initialSnapshots[accountId]!;
     final store = PerAccountStore.fromInitialSnapshot(
       globalStore: this,