Singleton and unit testing

Question

The Effective Java has the following statement on unit testing singletons

Making a class a singleton can make it difficult to test its clients, as it’s im

Answer 1

As far as I know, a class implementing a Singleton cannot be extended (superclass constructor is always called implicitly and the constructor in a Singleton is private). If you want to mock a class you have to extend the class. As you see in this case it wouldn't be possible.