如何模拟返回OneOf<IServiceA，IServiceB>的方法？使用最小起订量

问：

在我的项目中，编写了一种服务解析器类的常用方法。其中公共方法返回 OneOf<IServiceA、IServiceB、IServiceC>。我无法嘲笑这种类行为。

private readonly IServiceA _serviceA;
private readonly IServiceB _serviceB;
private readonly IServiceC _serviceC;

public ProjectResolver(
    IServiceA serviceA,
    IServiceB serviceB,
    IServiceC serviceC
)
{
    _serviceA = serviceA;
    _serviceB = serviceB;
    _serviceC = serviceC;
}

...

public OneOf<IServiceA, IServiceB, IServiceC> GetServiceHandler(string Id)
{
    if (!_projectSettings.Projects.ContainsKey(Id))
        return new NotFound();

    return _projectSettings.Projects[Id] switch
    {
        "a" => (ServiceA)_serviceA,
        "b" => (ServiceB)_serviceB,
        "c" => (ServiceC)_serviceC,
        _ => throw new ArgumentOutOfRangeException(Id)
    };
}

我已经模拟了所有服务（IServiceA、IServiceB 和 IServiceC）和项目解析器类。在运行测试时，我遇到以下异常。

Exception while calling Path
System.InvalidCastException: Unable to cast object of type 'Castle.Proxies.IserviceA' to type 'ServiceA'.

我需要帮助来模拟这个 projectResolver 类。提前👍致谢