Mockito using argument matchers for when call on method with variable number of arguments

Question

I am attempting to use argument matchers inside a when call to a method that has a variable number of arguments (the ... thing in Java) without success. My code is below and I'll also list all of the lines I tried using to make this work.

import static org.mockito.Mockito.*;

public class MethodTest {
    public String tripleDot(String... args) {
        String sum = "";
        for (String i : args) {
            sum += i;
        }
        System.out.println(sum);

        return sum;
    }

    public static void main(String[] args) {
        try{
            MethodTest mt = mock(MethodTest.class);
            when(mt.tripleDot((String[])anyObject())).thenReturn("Hello world!");
            System.out.println(mt.tripleDot(new String[]{"1","2"}));
        }
        catch (Exception e) {
            System.out.println(e.getClass().toString() + ": " + e.getMessage());
        }
    }
}

If print statement is:

System.out.println(mt.tripleDot(new String[]{"1"}));

or

System.out.println(mt.tripleDot("1"));

It will print "Hello world."

But if the print statement is:

System.out.println(mt.tripleDot(new String[]{"1","2"}));

or

System.out.println(mt.tripleDot("1","2"));

It will print "null".

I've also tried doing variations in the when call, such as anyObject() or anyString() but to no avail. I'm not sure if Mockito can handle using argument matchers in regard to method calls that include a variable number of arguments. Is it even possible? If so, what should I be doing to make this work?

Answer 1

Try the anyVararg() matcher. This was introduced in 1.8.1.