Get types used inside a specific class

Here's the class, which I want to get a list of all types used in it:

public class TestClass : MonoBehaviour{
    private UIManager _manager;

    private void Initialize(UIManager manager){
        _manager = manager;
    }
}

Then I thought that by running something like this:

    Assembly assembly = typeof (TestClass).Assembly;
    foreach (Type type in assembly.GetTypes()){
        Debug.Log(type.FullName);
    }

Would give me just the UIManager type. But instead it seems like it's giving me the list of all types used on my project.

How can I get just the types used on this class?

(as you can see TestClass inherits from MonoBehaviour, but I don't want the types used there, I want the types used specifically in TestClass).