Failing Tests

Four approaches to writing a test that expects an exception to occur:

• Approach 1:

  public void failGetter() throws IllegalArgumentException { 
      new Foo(null).getMember(); 
  } 



• Approach 2:

  public void testGetter2() { 
      String msg = ThrowAssert.assertThrows(IllegalArgumentException.class, new Block() { 
          public void call() throws Exception { 
              new Foo(null).getMember(); 
          } 
      }); 
  } 



• Approach 3:

  public void testGetter3() { 
      Foo foo = new Foo(null); 
      String msg = ThrowAssert.assertThrows(IllegalArgumentException.class, foo, 
          new CallSpec("getMember", new Class[]{}, new Object[] {null})); 
  } 



• Approach 4:

  public void testGetter4() { 
      try { 
          new Foo(null).getMember(); 
          fail("Expected NPE"); 
      } catch (NullPointerException npe) { 
          // We expect this to happen. 
      } catch (Exception e) { 
          fail("Wrong exception thrown"); 
      } 
  } 

I generally prefer Approach 2 because it is more extensible, use it when:

• There are multiple assertions to be checked and complicated calling is expected.


• Multiple exceptions are thrown, you can ignore any exception including checked exceptions.


• Assertions need to be made on the message from the thrown exception.


• There needs to be an opposing assertion - a test that it doesn't throw an exception (assertPasses).


• Variables can be made final.

Approach 1 can be used when the intent and code can be expressed on one line and only one exception is expected. It also requires there to be a bit of code in a test base class although it is inconsistent with the usual "textXXX" method names used for test code.