How do you assert that a certain exception is thrown in JUnit 4 tests?

Question

How can I use JUnit4 idiomatically to test that some code throws an exception?

While I can certainly do something like this:

@Test
public void testFo         


        

Answer 1

in junit, there are four ways to test exception.

junit5.x

• for junit5.x, you can use assertThrows as following

  @Test
  public void testFooThrowsIndexOutOfBoundsException() {
      Throwable exception = assertThrows(IndexOutOfBoundsException.class, () -> foo.doStuff());
      assertEquals("expected messages", exception.getMessage());
  }
  

junit4.x

• for junit4.x, use the optional 'expected' attribute of Test annonation

  @Test(expected = IndexOutOfBoundsException.class)
  public void testFooThrowsIndexOutOfBoundsException() {
      foo.doStuff();
  }
  

• for junit4.x, use the ExpectedException rule

  public class XxxTest {
      @Rule
      public ExpectedException thrown = ExpectedException.none();
  
      @Test
      public void testFooThrowsIndexOutOfBoundsException() {
          thrown.expect(IndexOutOfBoundsException.class)
          //you can test the exception message like
          thrown.expectMessage("expected messages");
          foo.doStuff();
      }
  }
  

• you also can use the classic try/catch way widely used under junit 3 framework

  @Test
  public void testFooThrowsIndexOutOfBoundsException() {
      try {
          foo.doStuff();
          fail("expected exception was not occured.");
      } catch(IndexOutOfBoundsException e) {
          //if execution reaches here, 
          //it indicates this exception was occured.
          //so we need not handle it.
      }
  }
  

• so

  • if you like junit 5, then you should like the 1st one
  • the 2nd way is used when you only want test the type of exception
  • the first and last two are used when you want test exception message further
  • if you use junit 3, then the 4th one is preferred

• for more info, you can read this document and junit5 user guide for details.