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A collection of JUnit rules for testing code which uses java.lang.System.
There is a newer version: 1.19.0
package org.junit.contrib.java.lang.system;

import static java.lang.System.clearProperty;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

import org.junit.contrib.java.lang.system.internal.RestoreSpecificSystemProperties;
import org.junit.rules.ExternalResource;

/**
 * The {@code ProvideSystemProperty} rule provides an arbitrary value for a
 * system property to a test. After the test the original value is restored. You
 * can ensure that a property is not set by providing {@code null} (or using
 * {@link org.junit.contrib.java.lang.system.ClearSystemProperties}).
 * 
 * Let's assume the system property {@code MyProperty} is not set and the system
 * property {@code OtherProperty} has the value {@code OtherValue}. Now run the
 * test
 *
 * 
 *   public void MyTest {
 *     @Rule
 *     public final ProvideSystemProperty provideSystemProperty
 *       = new ProvideSystemProperty("MyProperty", "MyValue")
 *         .and("OtherProperty", null);
 *
 *     @Test
 *     public void overridesProperty() {
 *       assertEquals("MyValue", System.getProperty("MyProperty"));
 *     }
 *
 *     @Test
 *     public void deletesProperty() {
 *       assertNull(System.getProperty("OtherProperty"));
 *     }
 *   }
 * 
 *
 * Both tests succeed and after the tests, the system property
 * {@code MyProperty} is not set and the system property {@code OtherProperty}
 * has the value {@code OtherValue}.
 * 
 * You can use a properties file to supply properties for the
 * ProvideSystemProperty rule. The file can be from the file system or the class
 * path. In the first case use
 *
 * 
 * @Rule
 * public final ProvideSystemProperty properties = ProvideSystemProperty
 * 		.fromFile("/home/myself/example.properties");
 * 
 *
 * and in the second case use
 *
 *  * @Rule
 * public final ProvideSystemProperty properties = ProvideSystemProperty
 * 		.fromResource("example.properties");
 * 
 * Set property for a single test
 * If you want to set a property for a single test then you can use
 * {@link org.junit.contrib.java.lang.system.RestoreSystemProperties}
 * along with {@link System#setProperty(String, String)}.
 * 
 * @Rule
 * public final TestRule restoreSystemProperties
 *   = new RestoreSystemProperties();
 *
 * @Test
 * public void test() {
 *   System.setProperty("YourProperty", "YourValue");
 *   ...
 * }
 */
public class ProvideSystemProperty extends ExternalResource {
	private final Map properties = new LinkedHashMap();
	private final RestoreSpecificSystemProperties restoreSystemProperty = new RestoreSpecificSystemProperties();

	public static ProvideSystemProperty fromFile(String name) {
		try {
			FileInputStream fis = new FileInputStream(name);
			return fromInputStream(fis);
		} catch (IOException e) {
			throw new IllegalArgumentException(
				"Cannot create ProvideSystemProperty rule because file \""
					+ name + "\" cannot be read.",
				e);
		}
	}

	public static ProvideSystemProperty fromResource(String name) {
		InputStream is = ProvideSystemProperty.class.getResourceAsStream(name);
		try {
			return fromInputStream(is);
		} catch (IOException e) {
			throw new IllegalArgumentException(
				"Cannot create ProvideSystemProperty rule because resource \""
					+ name + "\" cannot be read.",
				e);
		}
	}

	private static ProvideSystemProperty fromInputStream(InputStream is)
		throws IOException {
		Properties p = new Properties();
		p.load(is);
		ProvideSystemProperty rule = new ProvideSystemProperty();
		for (Map.Entry property : p.entrySet())
			rule.addProperty((String) property.getKey(),
				(String) property.getValue());
		return rule;
	}

	/**
	 * @deprecated see {@link #setProperty(String, String)}.
	 */
	@Deprecated
	public ProvideSystemProperty() {
	}

	/**
	 * Sets the property with the name to the specified value. After the test
	 * the rule restores the value of the property at the point of setting it.
	 *
	 * This method is deprecated. If you're still using it, please replace your current code
	 * 
	 * @Rule
	 * public final ProvideSystemProperty provideSystemProperty = new ProvideSystemProperty();
	 *
	 * @Test
	 * public void test() {
	 *   provideSystemProperty.setProperty("YourProperty", "YourValue");
	 *   ...
	 * }
	 * with this code:
	 * 	 * @Rule
	 * public final TestRule restoreSystemProperties = new RestoreSystemProperties();
	 *
	 * @Test
	 * public void test() {
	 *   System.setProperty("YourProperty", "YourValue");
	 *   ...
	 * }
	 *
	 * @param name the name of the property.
	 * @param value the new value of the property.
	 * @since 1.6.0
	 * @deprecated Please use {@link org.junit.contrib.java.lang.system.RestoreSystemProperties}
	 * along with {@link System#setProperty(String, String)}.
	 */
	@Deprecated
	public void setProperty(String name, String value) {
		restoreSystemProperty.add(name);
		if (value == null)
			clearProperty(name);
		else
			System.setProperty(name, value);
	}

	public ProvideSystemProperty(String name, String value) {
		addProperty(name, value);
	}

	public ProvideSystemProperty and(String name, String value) {
		addProperty(name, value);
		return this;
	}

	private void addProperty(String name, String value) {
		properties.put(name, value);
	}

	@Override
	protected void before() throws Throwable {
		setProperties();
	}

	private void setProperties() {
		for (Entry property : properties.entrySet()) {
			String name = property.getKey();
			String value = property.getValue();
			setProperty(name, value);
		}
	}

	@Override
	protected void after() {
		restoreSystemProperty.restore();
	}
}