I have injected IFlurlClient and i want to write test for it but it throw null refrence exception?

[Shirin Monzavi]

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here is sut;

public class CustomerService : ICustomerService
{
    private readonly IFlurlClient _flurlClient;
    private readonly ILoggerProvider<CustomerService> _logger;
    private readonly IConfiguration _configuration;

    public CustomerService(ILoggerProvider<CustomerService> logger, IConfiguration configuration, IFlurlClient flurlClient)
    {
        _logger = logger;
        _configuration = configuration;
        _flurlClient = flurlClient;
    }

    public async Task<int> PostCustomerData(GetCustomerOutputDto getCustomerOutputDtos)
    {
        try
        {
            var baseUrl = _configuration["ExternalSerivce:BaseUrl"];
            var segmentUrl = _configuration["ExternalSerivce:CustomerSegmentUrl"];

            _flurlClient.BaseUrl = baseUrl;

            var response = await
                _flurlClient
                .Request(segmentUrl)
                .PostJsonAsync(getCustomerOutputDtos);

            var s=await response.GetJsonAsync<PostResponse>();

            return s.Data;

        }
        catch (FlurlHttpException ex)
        {
            _logger.Information(getCustomerOutputDtos, $"Error returned from {ex.Call.Request.Url} {ex.Message}", string.Empty);
            return 0;
        }
    }
}

here is test class

public class CustomerServiceTests
{
    #region Feilds
    private readonly CustomerService sut;
    private readonly Mock<ILoggerProvider<CustomerService>> loggerMock;
    private readonly Mock<IConfiguration> configurationMock;
    private readonly Mock<IFlurlClient> flurlMock;
    private readonly Mock<IFlurlRequest> flurlRequestMock;
    private readonly Mock<IFlurlResponse> flurlResponseMock;
    #endregion

    public CustomerServiceTests()
    {
        loggerMock = new Mock<ILoggerProvider<CustomerService>>();
        configurationMock = new Mock<IConfiguration>();
        flurlMock = new Mock<IFlurlClient>();
        flurlRequestMock = new Mock<IFlurlRequest>();
        flurlResponseMock = new Mock<IFlurlResponse>();

        var settingsContainer = new Mock<ISettingsContainer>();

        configurationMock.Setup(c => c["ExternalSerivce:BaseUrl"]).Returns(CustomerExternaleServiceConstantTest.BASE_URL);
        configurationMock.Setup(c => c["ExternalSerivce:CustomerSegmentUrl"]).Returns(CustomerExternaleServiceConstantTest.CUSTOMER_SEGMENT_URL);

        flurlMock.Setup(c => c.Request(It.IsAny<string>())).Returns(flurlRequestMock.Object);
        flurlMock.Setup(c => c.BaseUrl).Returns(CustomerExternaleServiceConstantTest.BASE_URL);

        var httpMessageHandlerMock = new Mock<HttpMessageHandler>();

        flurlMock.Setup(c => c.HttpClient).Returns(new HttpClient(httpMessageHandlerMock.Object)
        {
            BaseAddress = new Uri(CustomerExternaleServiceConstantTest.BASE_URL),
            DefaultRequestVersion = new Version(),
            DefaultVersionPolicy = new HttpVersionPolicy(),
            MaxResponseContentBufferSize = 10,
            Timeout = TimeSpan.FromSeconds(10)
        });

        flurlRequestMock.Setup(c => c.Settings).Returns(new FlurlHttpSettings());

        flurlRequestMock.Setup(c => c.Url).Returns(new Flurl.Url(CustomerExternaleServiceConstantTest.BASE_URL));
        flurlRequestMock.Setup(c => c.Client).Returns(flurlMock.Object);
        flurlRequestMock.Setup(c => c.Verb).Returns(HttpMethod.Post);
        flurlRequestMock.Setup(c => c.CookieJar).Returns(new CookieJar());

        flurlResponseMock.Setup(c => c.ResponseMessage).Returns(new HttpResponseMessage()
        {
            StatusCode = HttpStatusCode.OK,
            Content = new StringContent("[{'id':1,'value':'1'}]"),
            ReasonPhrase = "",
            RequestMessage = new HttpRequestMessage(),
            Version = new Version()
        });
        var HttpContentMock = new Mock<HttpContent>();

        flurlResponseMock.Setup(c => c.StatusCode).Returns(200);
        sut = new CustomerService(loggerMock.Object, configurationMock.Object, flurlMock.Object);
    }

    [Fact]
    public async Task PostCustomerData_Should_Post_Customer_Data()
    {
        //Arrenge
        var customersData = new GetCustomerOutputDto()
        {
            GetCusTellDto = new List<GetCusTellDto>(),
            GetCustomerDto = new List<GetCustomerDto>(),
            GetSarfaslDto = new List<GetSarfaslDto>()
        };


        //Act
        var actual = await sut.PostCustomerData(customersData);

        //Assert
        actual.Should().BePositive();
    }

    public class HttpMessageHandlerMock : HttpMessageHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(
            HttpRequestMessage request,
            CancellationToken cancellationToken)
        {
            return Task.FromResult(new HttpResponseMessage());
        }
    }
}

PostJsonAsync method return null.
anyone can help?

[Todd Menier]

Please post programming questions on Stack Overflow. And it's going to be very difficult for anyone to help you unless you reduce this to a minimal reproducible example.