public class Calculator {
    public int result = 0;

    public int add(int operandl, int operand2) {
        result = operandl + operand2;
        return result;
    }

    public int subtract(int operandl, int operand2) {
        result = operandl - operand2;
        return result;
    }

    public int multiple(int operandl, int operand2) {
        result = operandl * operand2;
        for (; ; ) {

        }
    }

    public int divide(int operandl, int operand2) {
        result = operandl / 0;
        return result;
    }

    public int getResult() {
        return this.result;
    }

}

public class CalculatorTest {
    public static Calculator cal = new Calculator();

    //测试开始前只能被执行一次
    @BeforeClass
    public static void setUpBeforClass() throws Exception {
        System.out.println(" @BeforeClass");

    }

    //测试结束前只调用一次
    @AfterClass
    public static void tearDownAfterClass() throws Exception {
        System.out.println("@AfterClass");
    }

    @Before
    public void setUp() throws Exception {
        System.out.println("测试开始");
    }

    @After
    public void tearDown() throws Exception {
        System.out.println("测试结束");
    }

    @Test
    public void testSubstract() {
        cal.subtract(4, 2);
        assertEquals(2, cal.getResult());
//        fail("Not yet implemented");
    }

    @Test
    public void testAdd() {
        cal.add(2, 2);
        assertEquals(4, cal.getResult());
//        fail("Not yet implemented");
    }

    //忽略执行
    @Ignore
    public void testMultiply() {
        fail("Not yet implemented");

    }

    //测试用例时间不能超过2s，死循环时间超过2s
    @Test(timeout = 2000)
    public void testDivide() {
        for (; ; ) ;
    }

    //执行之后抛出异常才成功
    @Test(expected = ArithmeticException.class)
    public void testDivideByZero() {
        cal.divide(4, 0);
    }

}

单元测试JUnit4 Ctrl + Shift + T