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Spring Framework example source code file (AssertThrows.java)

This example Spring Framework source code file (AssertThrows.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

assertionfailederror, assertthrows, assertthrows, class, exception, exception, illegalargumentexception, should, string, string, stringbuffer, stringbuffer, the, was

The Spring Framework AssertThrows.java source code

/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.test;

import junit.framework.Assert;
import junit.framework.AssertionFailedError;

/**
 * Simple method object encapsulation of the 'test-for-Exception' scenario (for JUnit).
 *
 * <p>Used like so:
 *
 * <pre class="code">
 * // the class under test
 * public class Foo {
 *    public void someBusinessLogic(String name) {
 *        if (name == null) {
 *            throw new IllegalArgumentException("The 'name' argument is required");
 *        }
 *        // rest of business logic here...
 *    }
 * }</pre>
 *
 * The test for the above bad argument path can be expressed using the
 * {@link AssertThrows} class like so:
 *
 * <pre class="code">
 * public class FooTest {
 *    public void testSomeBusinessLogicBadArgumentPath() {
 *        new AssertThrows(IllegalArgumentException.class) {
 *            public void test() {
 *                new Foo().someBusinessLogic(null);
 *            }
 *        }.runTest();
 *    }
 * }</pre>
 *
 * This will result in the test passing if the <code>Foo.someBusinessLogic(..)
 * method threw an {@link java.lang.IllegalArgumentException}; if it did not, the
 * test would fail with the following message:
 *
 * <pre class="code">
 * "Must have thrown a [class java.lang.IllegalArgumentException]"</pre>
 *
 * If the <b>wrong type of {@link java.lang.Exception} was thrown, the
 * test will also fail, this time with a message similar to the following:
 *
 * <pre class="code">
 * "junit.framework.AssertionFailedError: Was expecting a [class java.lang.UnsupportedOperationException] to be thrown, but instead a [class java.lang.IllegalArgumentException] was thrown"</pre>
 *
 * The test for the correct {@link java.lang.Exception} respects polymorphism,
 * so you can test that any old {@link java.lang.Exception} is thrown like so:
 *
 * <pre class="code">
 * public class FooTest {
 *    public void testSomeBusinessLogicBadArgumentPath() {
 *        // any Exception will do...
 *        new AssertThrows(Exception.class) {
 *            public void test() {
 *                new Foo().someBusinessLogic(null);
 *            }
 *        }.runTest();
 *    }
 * }</pre>
 *
 * You might want to compare this class with the
 * {@link junit.extensions.ExceptionTestCase} class.
 *
 * <p>Note: This class requires JDK 1.4 or higher.
 *
 * @author Rick Evans
 * @author Juergen Hoeller
 * @since 2.0
 */
public abstract class AssertThrows {

	private final Class expectedException;

	private String failureMessage;

	private Exception actualException;


	/**
	 * Create a new instance of the {@link AssertThrows} class.
	 * @param expectedException the {@link java.lang.Exception} expected to be
	 * thrown during the execution of the surrounding test
	 * @throws IllegalArgumentException if the supplied <code>expectedException is
	 * <code>null; or if said argument is not an {@link java.lang.Exception}-derived class
	 */
	public AssertThrows(Class expectedException) {
		this(expectedException, null);
	}

	/**
	 * Create a new instance of the {@link AssertThrows} class.
	 * @param expectedException the {@link java.lang.Exception} expected to be
	 * thrown during the execution of the surrounding test
	 * @param failureMessage the extra, contextual failure message that will be
	 * included in the failure text if the text fails (can be <code>null)
	 * @throws IllegalArgumentException if the supplied <code>expectedException is
	 * <code>null; or if said argument is not an {@link java.lang.Exception}-derived class
	 */
	public AssertThrows(Class expectedException, String failureMessage) {
		if (expectedException == null) {
			throw new IllegalArgumentException("The 'expectedException' argument is required");
		}
		if (!Exception.class.isAssignableFrom(expectedException)) {
			throw new IllegalArgumentException(
					"The 'expectedException' argument is not an Exception type (it obviously must be)");
		}
		this.expectedException = expectedException;
		this.failureMessage = failureMessage;
	}


	/**
	 * Return the {@link java.lang.Exception} expected to be thrown during
	 * the execution of the surrounding test.
	 */
	protected Class getExpectedException() {
		return this.expectedException;
	}

	/**
	 * Set the extra, contextual failure message that will be included
	 * in the failure text if the text fails.
	 */
	public void setFailureMessage(String failureMessage) {
		this.failureMessage = failureMessage;
	}

	/**
	 * Return the extra, contextual failure message that will be included
	 * in the failure text if the text fails.
	 */
	protected String getFailureMessage() {
		return this.failureMessage;
	}


	/**
	 * Subclass must override this <code>abstract method and
	 * provide the test logic.
	 * @throws Exception if an error occurs during the execution of the
	 * aformentioned test logic
	 */
	public abstract void test() throws Exception;


	/**
	 * The main template method that drives the running of the
	 * {@link #test() test logic} and the
	 * {@link #checkExceptionExpectations(Exception) checking} of the
	 * resulting (expected) {@link java.lang.Exception}.
	 * @see #test() 
	 * @see #doFail()
	 * @see #checkExceptionExpectations(Exception)
	 */
	public void runTest() {
		try {
			test();
			doFail();
		}
		catch (Exception actualException) {
			this.actualException = actualException;
			checkExceptionExpectations(actualException);
		}
	}

	/**
	 * Template method called when the test fails; i.e. the expected
	 * {@link java.lang.Exception} is <b>not thrown.
	 * <p>The default implementation simply fails the test via a call to
	 * {@link junit.framework.Assert#fail(String)}.
	 * <p>If you want to customise the failure message, consider overriding
	 * {@link #createMessageForNoExceptionThrown()}, and / or supplying an
	 * extra, contextual failure message via the appropriate constructor overload.
	 * @see #getFailureMessage()
	 */
	protected void doFail() {
		Assert.fail(createMessageForNoExceptionThrown());
	}

	/**
	 * Creates the failure message used if the test fails
	 * (i.e. the expected exception is not thrown in the body of the test).
	 * @return the failure message used if the test fails
	 * @see #getFailureMessage()
	 */
	protected String createMessageForNoExceptionThrown() {
		StringBuffer sb = new StringBuffer();
		sb.append("Should have thrown a [").append(this.getExpectedException()).append("]");
		if (getFailureMessage() != null) {
			sb.append(": ").append(getFailureMessage());
		}
		return sb.toString();
	}

	/**
	 * Does the donkey work of checking (verifying) that the
	 * {@link java.lang.Exception} that was thrown in the body of a test is
	 * an instance of the {@link #getExpectedException()} class (or an
	 * instance of a subclass).
	 * <p>If you want to customise the failure message, consider overriding
	 * {@link #createMessageForWrongThrownExceptionType(Exception)}.
	 * @param actualException the {@link java.lang.Exception} that has been thrown
	 * in the body of a test method (will never be <code>null)
	 */
	protected void checkExceptionExpectations(Exception actualException) {
		if (!getExpectedException().isAssignableFrom(actualException.getClass())) {
			AssertionFailedError error =
					new AssertionFailedError(createMessageForWrongThrownExceptionType(actualException));
			error.initCause(actualException);
			throw error;
		}
	}

	/**
	 * Creates the failure message used if the wrong type
	 * of {@link java.lang.Exception} is thrown in the body of the test.
	 * @param actualException the actual exception thrown
	 * @return the message for the given exception
	 */
	protected String createMessageForWrongThrownExceptionType(Exception actualException) {
		StringBuffer sb = new StringBuffer();
		sb.append("Was expecting a [").append(getExpectedException().getName());
		sb.append("] to be thrown, but instead a [").append(actualException.getClass().getName());
		sb.append("] was thrown.");
		return sb.toString();
	}


	/**
	 * Expose the actual exception thrown from {@link #test}, if any.
	 * @return the actual exception, or <code>null if none
	 */
	public final Exception getActualException() {
		return this.actualException;
	}

}

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