testcase.dart

// Function to test //
Future<List<Contact>> fetchContacts(http.Client client) async {
  final response = await client.get(Uri.parse(url));
  if (response.statusCode == 200) {
    if (json.decode(response.body).toString().length > 2) {
      List jsonResponse = json.decode(response.body);
      return jsonResponse.map((e) => Contact.fromJson(e)).toList();
    } else {
      throw Exception('Failed to load contacts');
    }
  }
  throw Exception('Failed to load contacts');
}
// test case//
test('throws an exception if http call returns empty list', () async {
final client = MockClient((request) async {
  return Response(jsonEncode({}), 200);
});
expect(await fetchContacts(client),
    throw Exception('Failed to load contacts'));
});