JUnit: Possible to 'expect' a wrapped exception?

Question

I know that one can define an \'expected\' exception in JUnit, doing:

@Test(expect=MyException.class)
public void someMethod() { ... }
         


        

Answer 1

I wrote a little JUnit extension for that purpose. A static helper function takes a function body and an array of expected exceptions:

import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;

import java.util.Arrays;

public class AssertExt {
    public static interface Runnable {
        void run() throws Exception;
    }

    public static void assertExpectedExceptionCause( Runnable runnable, @SuppressWarnings("unchecked") Class[] expectedExceptions ) {
        boolean thrown = false;
        try {
            runnable.run();
        } catch( Throwable throwable ) {
            final Throwable cause = throwable.getCause();
            if( null != cause ) {
                assertTrue( Arrays.asList( expectedExceptions ).contains( cause.getClass() ) );
                thrown = true;
            }
        }
        if( !thrown ) {
            fail( "Expected exception not thrown or thrown exception had no cause!" );
        }
    }
}

You can now check for expected nested exceptions like so:

import static AssertExt.assertExpectedExceptionCause;

import org.junit.Test;

public class TestExample {
    @Test
    public void testExpectedExceptionCauses() {
        assertExpectedExceptionCause( new AssertExt.Runnable(){
            public void run() throws Exception {
                throw new Exception( new NullPointerException() );
            }
        }, new Class[]{ NullPointerException.class } );
    }
}

This saves you writing the same boiler plate code again and again.