How do I test an asmx webservice function with a complex object being its parameter?

I have a webservice with a parameter of type class e.g.

[Webmethod]
public string functionA(ClsParams objParam)
{

}

The class has reference to another class object in it and functions.

Now before handing it over to the client, I want to test it. I don't want to develop a UI for this but want to use the default asmx testing UI that appears in browser but for complex objects it is not giving me the text boxes like it does in case of params like string param1, string param2 to the function.

How do I test it?