Whenever you create a class in MATLAB it will be a Value class by default. However, while working with MATLAB Engine for python you can only use MATLAB Handle classes, which is mentioned in the link below
So in order to make the above example work, you will have to make your class a handle class which can be done by replacing the first line of your MATLAB code to
Another thing to note here is that the function signature of ADD_1 indicates that it needs 3 inputs: Test1 Object(this), first number(i1) and second number(i2). So inside your python script, you will have to create an object for Test1 and pass it as the first argument of ADD_1
myobj = eng.Test1()
func1_out = end.ADD_1(myobj, 10, 20)
I believe that the above changes should resolve your issue.