public async Task TestJsonFilePost()
        {
            //arrange
            var service = new RestService();
            var json = "{\"content\":\"hallo welt\"}";
            var fileName = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Assets/content.config");
            var str = File.ReadAllBytes(fileName);

            //act
            var res = await service.PostJsonAsync(new Uri(_testUri), json, new List<RestFile>()
            {
                new RestFile() { Content = str, ContentName = "fileContent", FileName = "fileName"}
            });

            //assert
            Assert.IsTrue(res.IsRequestSuccessfull, res.Exception?.ToString());
            if (res.IsRequestSuccessfull)
            {
                var response = await res.GetResponseAsStringAsync();
                File.WriteAllText(Path.Combine(AppDomain.CurrentDomain.BaseDirectory,
                    "Assets/response_json.txt"), response);

                //assert
                Assert.IsTrue(response.Contains("hallo welt"));
                Assert.IsTrue(response.Contains("content"));
                Assert.IsTrue(response.Contains("fileName"));
                Assert.IsTrue(response.StartsWith("start"));
                Assert.IsTrue(response.EndsWith("end"));
            }
        }
        public async Task TestJsonPost()
        {
            //arrange
            var service = new RestService();
            var json = "{\"content\":\"hallo welt\"}";
        
            //act
            var res = await service.PostJsonAsync(new Uri(_testUri), json);

            //assert
            Assert.IsTrue(res.IsRequestSuccessfull, res.Exception?.ToString());
            if (res.IsRequestSuccessfull)
            {
                var response = await res.GetResponseAsStringAsync();

                //assert
                Assert.IsTrue(response.Contains(json));
                Assert.IsTrue(response.StartsWith("start"));
                Assert.IsTrue(response.EndsWith("end"));
            }
        }