EnumTester.java

/* Copyright 2013 Jonatan Jönsson
 *
 *    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 se.softhouse.common.testlib;

import static org.fest.assertions.Assertions.assertThat;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import javax.annotation.concurrent.Immutable;

/**
 * Calls the compiler generated valueOf/toString methods for code coverage
 */
@Immutable
public final class EnumTester
{
	private EnumTester()
	{
	}

	/**
	 * Tests that the {@link Object#toString()} for each enum constant in {@code enumClass} returns
	 * the exact same as {@link Enum#name()} (default behavior).
	 * This guarantees that {@link Enum#valueOf(Class, String)} will work for each enum constant.
	 */
	public static <T extends Enum<T>> void testThatToStringIsCompatibleWithValueOf(Class<T> enumClass)
	{
		testThatToStringIsCompatibleWithValueOf(enumClass, false);
	}

	/**
	 * A variant of {@link #testThatToStringIsCompatibleWithValueOf(Class)} that doesn't care about
	 * the visibility of the {@code enumClass}
	 */
	public static <T extends Enum<T>> void testThatToStringIsCompatibleWithValueOfRegardlessOfVisibility(Class<T> enumClass)
	{
		testThatToStringIsCompatibleWithValueOf(enumClass, true);
	}

	private static <T extends Enum<T>> void testThatToStringIsCompatibleWithValueOf(Class<T> enumClass, boolean setAccessible)
	{
		Method compilerGeneratedMethod;
		try
		{
			compilerGeneratedMethod = enumClass.getMethod("valueOf", String.class);
			compilerGeneratedMethod.setAccessible(setAccessible);
		}
		catch(NoSuchMethodException e)
		{
			throw new IllegalArgumentException(enumClass.getSimpleName() + " is not an Enum", e);
		}
		for(T enumConstant : enumClass.getEnumConstants())
		{
			String toStringValue = enumConstant.toString();
			try
			{
				Object viaValueOf = compilerGeneratedMethod.invoke(null, toStringValue);
				assertThat(viaValueOf).isSameAs(enumConstant);
			}
			catch(IllegalAccessException e)
			{
				throw new IllegalArgumentException("Failed to access valueOf method on " + enumClass.getName(), e);
			}
			catch(InvocationTargetException e)
			{
				throw new IllegalArgumentException(enumClass.getName() + "#" + enumConstant.name() + "#valueOf() threw " + e.getCause()
						+ " for input: " + toStringValue, e);
			}
		}
	}
}