TestNG: How to test for mandatory exceptions?

Question

I'd like to write a TestNG test to make sure an exception is thrown under a specific condition, and fail the test if the exception is not thrown. Is there an easy way to do this without having to create an extra boolean variable?

A related blog post on this subject: http://konigsberg.blogspot.com/2007/11/testng-and-expectedexceptions-ive.html

Answer 1

@Test(expectedExceptions) is useful for the most common cases:

• You expect a specific exception to be thrown
• You need the message of that exception to contain specific words

Per the documentation a test will fail if no expectedException is thrown:

The list of exceptions that a test method is expected to throw. If no exception or a different than one on this list is thrown, this test will be marked a failure.

Here are a few scenarios where @Test(expectedExceptions) is not sufficient:

• Your test method has several statements and only one of them is expected to throw
• You are throwing your own type of exception and you need to make sure it matches a certain criterion

In such cases, you should just revert to the traditional (pre-TestNG) pattern:

try {   // your statement expected to throw   fail(); } catch(<the expected exception>) {   // pass } 

Answer 2

Use @Test annotation to check expected exceptions.

@Test(     expectedExceptions = AnyClassThatExtendsException.class,     expectedExceptionsMessageRegExp = "Exception message regexp" ) 

Or if you don't want to check for exception message, only below is enough

@Test(expectedExceptions = AnyClassThatExtendsException.class) 

In that way, you don't need to use ugly try catch block, just invoke you exception-thrower method inside the test.