public async Task Post_RegisterWithExistingUserShouldReturnBadRequestWithErrors()
        {
            var model = new TestRegisterInputModel()
            {
                UserName        = "******",
                Email           = "*****@*****.**",
                Password        = "******",
                ConfirmPassword = "******"
            };

            var response = await this.client.PostAsJsonAsync("/api/Identity/Register", model,
                                                             new JsonSerializerOptions()
            {
                IgnoreNullValues = true
            });

            Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);

            var result = await response.Content.ReadFromJsonAsync <List <string> >();

            Assert.NotEmpty(result);
            Assert.Equal(2, result.Count);
            Assert.Contains(result, e => e == "User name 'admin' is already taken.");
            Assert.Contains(result, e => e == "Email '*****@*****.**' is already taken.");
        }
        public async Task Post_RegisterWithInvalidModelShouldReturnBadRequest(TestRegisterInputModel model)
        {
            var response = await this.client.PostAsJsonAsync("/api/Identity/Register", model,
                                                             new JsonSerializerOptions()
            {
                IgnoreNullValues = true
            });

            Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
            Assert.Equal("application/problem+json", response.Content.Headers.ContentType.MediaType);
        }