如何模拟通用方法返回具体类型？

Question

I'm trying to mock the return type of a generic method to match a specific concrete type but I cannot seem to get the casting to work out:

    public T Get<T>(string key)
    {
        if (typeof(T) == typeof(GenericIsAuthenticatedResponse) && key == "1234")
            return GetGenericIsAuthenticatedResponse();

        return default(T);
    }

    private static GenericIsAuthenticatedResponse GetGenericIsAuthenticatedResponse()
    {
       return new GenericIsAuthenticatedResponse
        {
            AuthCode = "1234",
            Email = "email@email.com"
        };
    }

So my question is how can I get the mock method to return the GenericIsAuthenticatedResponse?

Answer 1

That does not work because of how generics work. If you want to return a specific type, you need to provide a filter for T :

public T Get<T>(string key) where T: GenericIsAuthenticatedResponse 

Otherwise, don't use generics for the return type:

public object Get<T>(string key)
{
    if (typeof(T) == typeof(GenericIsAuthenticatedResponse) && key == "1234")
        return GetGenericIsAuthenticatedResponse();

    return default(T);
}

If you are completely sure that T will be GenericIsAuthenticatedResponse (given it's a test), you can do this:

public T Get<T>(string key)
{
    if (typeof(T) == typeof(GenericIsAuthenticatedResponse) && key == "1234")
        return (T)GetGenericIsAuthenticatedResponse();

    return default(T);
}

Answer 2

I applied some lateral thinking in the end (or bodge depending on your POV) and serialised/deserialised Json to achieve this:

   public T Get<T>(string key)
    {
        if (typeof(T) == typeof(GenericIsAuthenticatedResponse) && key == "1234")
            return JsonConvert.DeserializeObject<T>(GetGenericIsAuthenticatedResponse());

        return default(T);
    }

    private static string GetGenericIsAuthenticatedResponse()
    {
        var r = new GenericIsAuthenticatedResponse
        {
            Username = "email.email.com",
            AuthCode = "1234"
        };

        return JsonConvert.SerializeObject(r);
    }