PowerMock: How to spy System.out.println?

Question

Let's say I have the following class:

class MyClass { 
    public MyClass(){
    }
    public void hello() {
       System.out.println("hello");
    }
}

and I want to test 'hello' method:

@Test
public void testHello() {
    MyClass mc = new MyClass();
    mc.hello();
}

Now, I want to spy System.out.println and make sure that this method was called with "hello" as argument. How do I do it?

Possible duplicate of [JUnit test for System.out.println()](https://stackoverflow.com/questions/1119385/junit-test-for-system-out-println) — Roland Weisleder, Feb 07 '19 at 16:22

score 2 · Accepted Answer · answered Feb 06 '19 at 13:23

System.out is actually an instance of PrintStream, so my approach would be to create a mock of this class and direct output to that using the System.setOut method:

PrintStream outMock = Mockito.mock(PrintStream.class);
System.setOut(outMock);
System.out.println("Hello");
Mockito.verify(outMock).println("Hello");

Remember to restore the previous PrintStream instance after the test, preferably in a finally clause.

PowerMock: How to spy System.out.println?

1 Answers1