UnitTest.java

public class HomeworkCentral {
    private final Homework homework;

    public HomeworkCentral(Homework homework) {
        this.homework = homework;
    }

    void doHomework() {
        homework.complete();
    }
}

[TestMethod]
public class HomeworkCentralTest {
    Homework homeworkMock = mock(Homework.class);
    
    public void complete_homework() {
        HomeworkCentral homeworkCentral = new HomeworkCentral(homeworkMock);
        homeworkCentral.doHomework();
        verify(homeworkMock).complete();
    }
}