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Faking & Mocking Java

Set Fake Singleton Example

Here's how we would implement Set Fake Singleton:

public class AppLog {
	private static AppLog log;
	public static AppLog singleInstance() {
		if (log == null)
			createInstance();
		return log;
	}
	public static void setSingleInstance(AppLog newLog) {
		log = newLog;
	}
}
public class SomethingTest {
	@Test
	public void testWhatever() {
		AppLog.setSingleInstance(new FakeAppLog());
		// … Any uses of AppLog will really use FakeAppLog.
	}
}
With this technique, tests replace the singleton. Thus, just like Alternate Construction, they run the same risk of replacing the log for everybody.
Take care to put the real singleton back for subsequent tests!
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