如何使用JUnit来测试某些代码是否抛出异常?

我当然可以这样做:

@Test
public void testFooThrowsIndexOutOfBoundsException() {
  boolean thrown = false;

  try {
    foo.doStuff();
  } catch (IndexOutOfBoundsException e) {
    thrown = true;
  }

  assertTrue(thrown);
}

我记得,对于这类情况,有一个注释或Assert.xyz之类的东西远没有JUnit那么笨拙,更符合JUnit的精神。


当前回答

我会使用assertThatTownBy

@Test
public void testFooThrowsIndexOutOfBoundsException() {
  assertThatThrownBy(() -> doStuff()).isInstanceOf(IndexOutOfBoundsException.class)
}

其他回答

try {
    my method();
    fail( "This method must thrwo" );
} catch (Exception ex) {
    assertThat(ex.getMessage()).isEqual(myErrormsg);
}

您也可以这样做:

@Test
public void testFooThrowsIndexOutOfBoundsException() {
    try {
        foo.doStuff();
        assert false;
    } catch (IndexOutOfBoundsException e) {
        assert true;
    }
}

JUnit框架具有assertThrows()方法:

ArithmeticException exception = assertThrows(ArithmeticException.class, () ->
    calculator.divide(1, 0));
assertEquals("/ by zero", exception.getMessage());

对于JUnit 5,它位于org.unit.jupiter.api.Assertions类中;对于JUnit 4.13,它位于org.JUnit.Assert类中;对于JUnit4的早期版本:只需将org.JUnit.jupiter:junitjupiterapi上的引用添加到项目中,就可以从JUnit5获得非常好的工作版本。

我们可以在必须返回异常的方法之后使用断言失败:

try{
   methodThatThrowMyException();
   Assert.fail("MyException is not thrown !");
} catch (final Exception exception) {
   // Verify if the thrown exception is instance of MyException, otherwise throws an assert failure
   assertTrue(exception instanceof MyException, "An exception other than MyException is thrown !");
   // In case of verifying the error message
   MyException myException = (MyException) exception;
   assertEquals("EXPECTED ERROR MESSAGE", myException.getMessage());
}

例如,您想为下面提到的代码片段编写Junit

public int divideByZeroDemo(int a,int b){

    return a/b;
}

public void exceptionWithMessage(String [] arr){

    throw new ArrayIndexOutOfBoundsException("Array is out of bound");
}

上面的代码用于测试可能发生的某些未知异常,下面的代码用于使用自定义消息断言某些异常。

 @Rule
public ExpectedException exception=ExpectedException.none();

private Demo demo;
@Before
public void setup(){

    demo=new Demo();
}
@Test(expected=ArithmeticException.class)
public void testIfItThrowsAnyException() {

    demo.divideByZeroDemo(5, 0);

}

@Test
public void testExceptionWithMessage(){


    exception.expectMessage("Array is out of bound");
    exception.expect(ArrayIndexOutOfBoundsException.class);
    demo.exceptionWithMessage(new String[]{"This","is","a","demo"});
}