void main() {
  late ApiManager apiManager;
  late MockHTTPClient mockHTTPClient;

  setUp(() {
    mockHTTPClient = MockHTTPClient();
    apiManager = ApiManager(mockHTTPClient);
  });
 test(
        'given UserRepository class when getUser function is called and status code is 200 then a usermodel should be returned',
        () async {
          // Arrange
          const mockResponse = '{"status": "200"}';
          String url = "url";
          when(() {
            return mockHTTPClient.post(Uri.parse(url));
          }).thenAnswer((invocation) => Future.delayed(Durations.short2,() => Response(mockResponse, 200),), );
          // Act
          final user = await apiManager.userLoginApi();
          // Assert
          expect(isuserExist, isA<Data()>());
        },
      );


Future<Data> userLoginApi({String? email, String? password}) async {
    final response = await client.post(
      Uri.parse('url'),
    );
    if (response.statusCode == 200) {
      Map<String, String> body = {
        "email": email.toString(),
        "password": password.toString()
      };
      return Data.fromJson(body);
    }
    throw Exception('Some Error Occurred');
  }

Getting this error ‘type ‘Null’ is not a subtype of type ‘Future.. Also, what should i pass in the body. It’s a user login api which includes email and pass. Since its a test case i cant pass the user credentials.