SetPublicPropretyTest.java

public void testSquare() {
    
    TerribleMathStudent terribleMathStudent = new TerribleMathStudent();
    terribleMathStudent.setCalculator(new BrokenCalculator());
    
    //terribleMathStudent uses broken calculator to do this, so this student really sucks
    int result = terribleMathStudent.square(2);
    
    assertNotEquals(result, 4);
    
    //we pity the terrible math student, so we give him a working calculator
    terribleMathStudent.setCalculator(new Calculator());
    
    result = terribleMathStudent.square(2);
    
    assertEquals(result, 4);
}