Csharp 单元测试：模拟返回空

我已经用同样的场景做了很多次了，但这一次失败了，我想不出原因，请帮帮我.

下面是我的代码，我已经try 了Moq和NSubsitute，但对于这两个，返回是null，但它应该返回json，我放在里面，我已经做了相同的在以前的项目，但从来没有遇到过这样的问题，我的头脑完全不工作.

public interface IMyInterface
{
    public string myOrder(List<Order> order);       
}

目标类

public class funcMyFunctionApp
{
    private readonly IMyInterface myInterface;
    private readonly TelemetryClient telemetryClient;
    private readonly ILogger _logger;

    public funcMyFunctionApp(IMyInterface _myInterface)
    {
        myInterface = _myInterface;
    }

    [FunctionName("func1")]
    public IActionResult func1([HttpTrigger(AuthorizationLevel.Function, "post",Route = "func1")] string jsoninput)
    {
        try
        {
            if (!string.IsNullOrEmpty(jsoninput))
            {
                return new OkObjectResult(myInterface.myOrder(JsonConvert.DeserializeObject<List<Order>>(jsoninput)));
            }
            else
            {
                return new BadRequestObjectResult("Bad Order");
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex.Message);
            if(ex.InnerException != null)
            {
                _logger.LogError(ex.InnerException.Message.ToString());
            }
            return new BadRequestObjectResult("Bad Order");
        }
    }
}

测试fixture

public void shouldReturnOkObjectResultifInputisValid()
{
    string ValidJson1 = @"[
        {
          ""CreatedBy"":""test@test.org"",
          ""OrderNo"":""Pizz111"",
          ""Amount"":""10$"",
        }
    ]";
    string ValidOutputJson1 = @"{
        ""OrderNo"": ""808098"",
        ""Item"": ""Pizza""
    }";
    Mock<IMyInterface> myInterfaceMock =new Mock<IMyInterface>();
    IMyInterface myInterfaceSubsititueMock = Substitute.For<IMyInterface>();
    var input = JsonConvert.DeserializeObject<List<Order>>(ValidJson1);
    myInterfaceMock.Setup(m=>m.myOrder(input)).Returns(ValidOutputJson1);
    
    //Local Arrange
    myInterfaceSubsititueMock.myOrder(ValidJson1).Returns(ValidOutputJson1);
    funcMyFunctionApp funcRequest = new funcMyFunctionApp(myInterfaceMock.Object);
    
    // Act
    var result = funcRequest.func1(ValidJson1);
    
    // Assert
    Assert.Multiple(() =>
    {
        Assert.That((((OkObjectResult)result).Value as string), Is.EqualTo(ValidOutputJson1));
    });
}  

我期望它应该返回Returns以下提供的字符串