How Can I Effectively Test for Exception Handling in JUnit?

Testing Exception Handling in JUnit

In JUnit, testing whether a specific exception is thrown can be achieved in multiple ways.

JUnit 5 and 4.13

The @Test annotation now supports the expected attribute, which allows you to specify the expected exception type:

@Test(expected = IndexOutOfBoundsException.class)
public void testIndexOutOfBoundsException() {
    ArrayList emptyList = new ArrayList();
    Object o = emptyList.get(0);
}

AssertJ or Google Truth

Third-party assertion libraries like AssertJ and Google Truth provide more concise syntax for exception testing:

// AssertJ
assertThatThrownBy(() -> foo.doStuff()).isInstanceOf(IndexOutOfBoundsException.class);

// Google Truth
assertWithMessage("Expected IndexOutOfBoundsException").thatExceptionOfType(IndexOutOfBoundsException.class).isThrownBy(() -> foo.doStuff());

JUnit <= 4.12

For JUnit 4.12 and earlier, there are several options:

1. Boolean flag: Similar to the code in the original question.
2. @Rule: The @Rule annotation can be used to create a test rule that asserts an exception is thrown.
3. Custom matchers: Create a custom Hamcrest matcher to check if an exception of a specific type was thrown.

Refer to the JUnit Test-FAQ for more details on these options.

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