ThrownMatcher is a Hamcrest matcher that can be used to verify a Throwable of a certain type has been thrown.

ThrownMatcher.java

package com.athaydes.automaton.internal;

import org.hamcrest.Description;
import org.hamcrest.Factory;
import org.hamcrest.Matcher;
import org.junit.internal.matchers.TypeSafeMatcher;

/**
 * User: Renato
 */
public class ThrownMatcher extends TypeSafeMatcher<Runnable> {

	private final String expected;
	private String actual;

	public ThrownMatcher( String s ) {
		expected = s;
	}

	@Factory
	public static Matcher<Runnable> thrown( Class<? extends Throwable> expected ) {
		return new ThrownMatcher( expected.getName() );
	}

	@Override
	public boolean matchesSafely( Runnable action ) {
		try {
			action.run();
			actual = "nothing";
			return false;
		} catch ( Throwable t ) {
			actual = t.getClass().getName();
			return actual.equals( expected );
		}
	}

	@Override
	public void describeTo( Description description ) {
		description.appendText( "Should have thrown " + expected + " but threw " + actual );
	}

}