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

As answered before, there are many ways of dealing with exceptions in JUnit. But with Java 8 there is another one: using Lambda Expressions. With Lambda Expressions we can achieve a syntax like this:

@Test
public void verifiesTypeAndMessage() {
    assertThrown(new DummyService()::someMethod)
            .isInstanceOf(RuntimeException.class)
            .hasMessage("Runtime exception occurred")
            .hasMessageStartingWith("Runtime")
            .hasMessageEndingWith("occurred")
            .hasMessageContaining("exception")
            .hasNoCause();
}

assertThrown accepts a functional interface, whose instances can be created with lambda expressions, method references, or constructor references. assertThrown accepting that interface will expect and be ready to handle an exception.

This is relatively simple yet powerful technique.

Have a look at this blog post describing this technique: http://blog.codeleak.pl/2014/07/junit-testing-exception-with-java-8-and-lambda-expressions.html

The source code can be found here: https://github.com/kolorobot/unit-testing-demo/tree/master/src/test/java/com/github/kolorobot/exceptions/java8

Disclosure: I am the author of the blog and the project.