test [nfc]: Simplify out TestGlobalStore.updateMachines

Thanks to the introduction of PerAccountStore.updateMachine
in be6698e, this feature in the test code is no longer needed.

Author: gnprice

test/model/store_test.dart

@@ -590,14 +590,13 @@ void main() {
 
   group('UpdateMachine.poll', () {
     late TestGlobalStore globalStore;
-    late UpdateMachine updateMachine;
     late PerAccountStore store;
+    late UpdateMachine updateMachine;
     late FakeApiConnection connection;
 
     void updateFromGlobalStore() {
-      updateMachine = globalStore.updateMachines[eg.selfAccount.id]!;
-      store = updateMachine.store;
-      assert(identical(store, globalStore.perAccountSync(eg.selfAccount.id)));
+      store = globalStore.perAccountSync(eg.selfAccount.id)!;
+      updateMachine = store.updateMachine!;
       connection = store.connection as FakeApiConnection;
     }
 
@@ -1005,9 +1004,8 @@ void main() {
       completers().single.complete(store);
       await future;
       completers().clear();
-      final updateMachine = globalStore.updateMachines[eg.selfAccount.id] =
-        UpdateMachine.fromInitialSnapshot(
-          store: store, initialSnapshot: eg.initialSnapshot());
+      final updateMachine = UpdateMachine.fromInitialSnapshot(
+        store: store, initialSnapshot: eg.initialSnapshot());
       updateMachine.debugPauseLoop();
       updateMachine.poll();
 

test/model/test_store.dart

@@ -124,8 +124,7 @@ mixin _DatabaseMixin on GlobalStore {
 ///
 /// Unlike with [LiveGlobalStore] and the associated [UpdateMachine.load],
 /// there is no automatic event-polling loop or other automated requests.
-/// For each account loaded, there is a corresponding [UpdateMachine]
-/// in [updateMachines], which tests can use for invoking that logic
+/// Tests can use [PerAccountStore.updateMachine] in order to invoke that logic
 /// explicitly when desired.
 ///
 /// See also [TestZulipBinding.globalStore], which provides one of these.
@@ -135,9 +134,6 @@ class TestGlobalStore extends GlobalStore with _ApiConnectionsMixin, _DatabaseMi
     required super.accounts,
   }) : super(globalSettings: globalSettings ?? eg.globalSettings());
 
-  /// A corresponding [UpdateMachine] for each loaded account.
-  final Map<int, UpdateMachine> updateMachines = {};
-
   final Map<int, InitialSnapshot> _initialSnapshots = {};
 
   static const Duration removeAccountDuration = Duration(milliseconds: 1);
@@ -174,7 +170,7 @@ class TestGlobalStore extends GlobalStore with _ApiConnectionsMixin, _DatabaseMi
       accountId: accountId,
       initialSnapshot: initialSnapshot,
     );
-    updateMachines[accountId] = UpdateMachine.fromInitialSnapshot(
+    UpdateMachine.fromInitialSnapshot(
       store: store, initialSnapshot: initialSnapshot);
     return Future.value(store);
   }