Testing a method with return type void

Question

I'm new to software testing. In a tutorial I read that I can test some methods like this:

@Test
 public void testMultiply() {
   MyClass tester = new MyClass();
   assertEquals("10 x 5 must be 50", 50, tester.multiply(10, 5));
 } 

So I have to pass some parameters to a method and get a return value.
But in my case I have some classes without any parameters and return values:

ArrayList al = new ArrayList();

public void Main(){
  methodA();
  methodB();
}

public void methodA(){
  // connect to URL
  // get some data
  for(int i=0; i<someThing; i++){
    al.add(data);
  }
}
public void methodB(){
  // do something with al
}

Is it also possible to test them? For example whether the right value comes from the URL in methodA().

Answer 1

It is possible to test methods that don't return anything (void), but you must test that method's side effects. It should have some side effects, otherwise such a method is useless.

The side effect here is that al is changed. As written, this class doesn't have any other methods that expose al. Add a getter method that returns either the ArrayList or a specific element of the ArrayList. Then your test method can call the getter method to retrieve the value(s) and compare it(them) with the expected value(s).