Mockito - how to verify that a mock was never invoked

I'm looking for a way to verify with Mockito, that there wasn't any interaction with a given mock during a test. It's easy to achieve that for a given method with verification mode never(), but I haven't found a solution for the complete mock yet.

What I actually want to achieve: verify in tests, that nothing get's printed to the console. The general idea with jUnit goes like that:

private PrintStream systemOut;

@Before
public void setUp() {
    // spy on System.out
    systemOut = spy(System.out);
}

@After
public void tearDown() {
    verify(systemOut, never());  // <-- that doesn't work, just shows the intention
}

A PrintStream has tons of methods and I really don't want to verify each and every one with separate verify - and the same for System.err...

So I hope, if there's an easy solution, that I can, given that I have a good test coverage, force the software engineers (and myself) to remove their (my) debug code like System.out.println("Breakpoint#1"); or e.printStacktrace(); prior to committing changes.

Solution 1:

Use this :

import static org.mockito.Mockito.verifyZeroInteractions;

// ...

private PrintStream backup = System.out;

@Before
public void setUp() {
    System.setOut(mock(PrintStream.class));
}

@After
public void tearDown() {
    verifyZeroInteractions(System.out);
    System.setOut(backup);
}

Solution 2:

verifyZeroInteractions(systemOut);

As noted in comments, this doesn't work with a spy.

For a roughly equivalent but more complete answer, see the answer by gontard to this question.

Solution 3:

Since the original correct answer, verifyZeroInteractions has been deprecated, use verifyNoInteractions instead:

import org.junit.jupiter.api.Test;

import static org.mockito.Mockito.*;

public class SOExample {

    @Test
    public void test() {
        Object mock = mock(Object.class);
        verifyNoInteractions(mock);
    }
}

Solution 4:

You could try a slightly different tack:

private PrintStream stdout;

@Before public void before() {
    stdout = System.out;
    OutputStream out = new OutputStream() {
        @Override public void write(int arg0) throws IOException {
            throw new RuntimeException("Not allowed");
        }
    };
    System.setOut(new PrintStream(out));
}

@After public void after() {
    System.setOut(stdout);
}

If you preferred, you could switch the anonymous type for a mock and verify as Don Roby suggests.