DogTest.java

import junit.framework.TestCase;
import org.junit.Test;
import org.mockito.ArgumentCaptor;

import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;

public class DogTest extends TestCase {

    @Test
    public void testBark() {

        // The argument to be tested should be called on a mocked class
        // i.e. we need to test the "lifeQuote" argument passed onto "Util" method "shoutOut"
        // therefore we should mock the Util class
        Util utilMock = mock(Util.class);

        Dog toby = new Dog(utilMock);
        toby.bark();

        // We need to create a captor to capture the argument
        // In our case, the captured argument is of type String
        ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);

        // Verify that the captor is used in the mocked method
        verify(utilMock).shoutOut(captor.capture());

        // Retrieve the captured value
        String updatedLifeQuote = captor.getValue();

        // Assert if the value is as expected
        assertEquals("I'm awesome", updatedLifeQuote);
    }

}