Added Google Drive storage location

test/merge_utils_test.dart

@@ -0,0 +1,54 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:fuel_tax_tracker/services/merge_utils.dart';
+
+class _Record {
+  final String id;
+  final String value;
+  final DateTime updatedAt;
+
+  _Record(this.id, this.value, this.updatedAt);
+}
+
+void main() {
+  group('mergeById', () {
+    test('unions records that only exist on one side', () {
+      final remote = [_Record('a', 'remote-a', DateTime(2024, 1, 1))];
+      final local = [_Record('b', 'local-b', DateTime(2024, 1, 1))];
+
+      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);
+
+      expect(result.map((r) => r.id), containsAll(['a', 'b']));
+      expect(result.length, 2);
+    });
+
+    test('keeps the newer updatedAt when a record exists on both sides', () {
+      final remote = [_Record('a', 'remote-old', DateTime(2024, 1, 1))];
+      final local = [_Record('a', 'local-new', DateTime(2024, 6, 1))];
+
+      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);
+
+      expect(result.length, 1);
+      expect(result.first.value, 'local-new');
+    });
+
+    test('keeps the remote copy when it is newer than local', () {
+      final remote = [_Record('a', 'remote-new', DateTime(2024, 6, 1))];
+      final local = [_Record('a', 'local-old', DateTime(2024, 1, 1))];
+
+      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);
+
+      expect(result.length, 1);
+      expect(result.first.value, 'remote-new');
+    });
+
+    test('local wins ties', () {
+      final sameTime = DateTime(2024, 1, 1);
+      final remote = [_Record('a', 'remote', sameTime)];
+      final local = [_Record('a', 'local', sameTime)];
+
+      final result = mergeById(remote, local, (r) => r.id, (r) => r.updatedAt);
+
+      expect(result.first.value, 'local');
+    });
+  });
+}