ExpectException.java

package org.junit.internal.runners.statements;

import org.junit.internal.AssumptionViolatedException;
import org.junit.runners.model.Statement;

public class ExpectException extends Statement {
    private final Statement next;
    private final Class<? extends Throwable> expected;

    public ExpectException(Statement next, Class<? extends Throwable> expected) {
        this.next = next;
        this.expected = expected;
    }

    @Override
    public void evaluate() throws Exception {
        boolean complete = false;
        try {
            next.evaluate();
            complete = true;
        } catch (AssumptionViolatedException e) {
            throw e;
        } catch (Throwable e) {
            if (!expected.isAssignableFrom(e.getClass())) {
                String message = "Unexpected exception, expected<"
                        + expected.getName() + "> but was<"
                        + e.getClass().getName() + ">";
                throw new Exception(message, e);
            }
        }
        if (complete) {
            throw new AssertionError("Expected exception: "
                    + expected.getName());
        }
    }
}