Add: GraphQl Test (PalisadoesFoundation#2298)

test/service_tests/graphql_config_test.dart

@@ -0,0 +1,33 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:graphql_flutter/graphql_flutter.dart';
+import 'package:talawa/services/graphql_config.dart';
+import '../helpers/test_helpers.dart';
+import '../helpers/test_locator.dart';
+
+void main() {
+  testSetupLocator();
+
+  setUp(() {
+    registerServices();
+  });
+  group('Testing Graphql Config', () {
+    test('test httpLink with MockHttpClient', () async {
+      final graphqlConfig = GraphqlConfig();
+      final mockHttpClient = MockHttpClient();
+      final mockUri = Uri.parse('https://example.com/graphql');
+
+      graphqlConfig.httpLink = HttpLink(
+        mockUri.toString(),
+        httpClient: mockHttpClient,
+      );
+
+      final response = await graphqlConfig
+          .clientToQuery()
+          .query(QueryOptions(document: gql('query {}')));
+      expect(
+        response.data,
+        isNull,
+      );
+    });
+  });
+}