捕获预期的异常

可以在没有任何 try catch 块的情况下轻松捕获异常。

public class ListTest {
  private final List<Object> list = new ArrayList<>();

  @Test(expected = IndexOutOfBoundsException.class)
  public void testIndexOutOfBoundsException() {
    list.get(0);
  }
}

当你不希望/需要检查抛出的异常所携带的消息时，上面的示例应该足以满足更简单的情况。

如果要检查有关异常的信息，可能需要使用 try / catch 块：

@Test
public void testIndexOutOfBoundsException() {
    try {
        list.get(0);
        Assert.fail("Should throw IndexOutOfBoundException");
    } catch (IndexOutOfBoundsException ex) {
        Assert.assertEquals("Index: 0, Size: 0", ex.getMessage());
    }
}

对于此示例，你必须注意始终添加 Assert.fail() 以确保在未抛出异常时测试将失败。

对于更详细的案例，JUnit 有 ExpectedException @Rule ，它也可以测试这些信息并按如下方式使用：

public class SimpleExpectedExceptionTest {
     @Rule
     public ExpectedException expectedException = ExpectedException.none();

     @Test
     public void throwsNothing() {
         // no exception expected, none thrown: passes.
     }

     @Test
     public void throwsExceptionWithSpecificType() {
         expectedException.expect(NullPointerException.class);

         throw new NullPointerException();
     }

     @Test
     public void throwsExceptionWithSpecificTypeAndMessage() {
         expectedException.expect(IllegalArgumentException.class);
         expectedException.expectMessage("Wanted a donut.");

         throw new IllegalArgumentException("Wanted a donut.");
     }
}

在 JUnit5 中测试异常

要在 JUnit 5 中实现相同的功能，请使用全新的机制 ：

测试方法

public class Calculator {
    public double divide(double a, double b) {
        if (b == 0.0) {
            throw new IllegalArgumentException("Divider must not be 0");
        }
        return a/b;
    }
}

该测试方法

public class CalculatorTest {
    @Test
    void triangularMinus5() { // The test method does not have to be public in JUnit5
        Calculator calc = new Calculator();

        IllegalArgumentException thrown = assertThrows(
            IllegalArgumentException.class, 
            () -> calculator.divide(42.0, 0.0));
        // If the exception has not been thrown, the above test has failed.

        // And now you may further inspect the returned exception...
        // ...e.g. like this:
        assertEquals("Divider must not be 0", thrown.getMessage());
}