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Unit testing Singletons and/or "static" classes and possible alternatives

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Mac IntelliJ IDE Java
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Greetings fellow Coderanchers,

I have some questions regarding unit testing singletons and/or "static" classes [in java] and what are the potential alternatives. I'm aware this is a loaded question so I'll try my best to funnel to my issue.

I'm currently creating a simple wrapper around some of the java.nio libraries so I can use them in my application. Here's the code for reference: (sorry for the link, the code is class is 103 lines).

One of the goals when I was writing this is that I wanted to get 100% coverage so as I wrote this class I also wrote unit tests until I hit a bump in the road here:

At this point I turned to mocking using Mockito and PowerMock so I could handle final classes as well as mocking static methods. Unfortunately, PowerMock is not intuitive and I kept getting an unresolvable error that seemed to have even stumped StackOverflow. Anyway, so I turned to a singleton:

I updated all my unit tests to reflection this change and my code coverage dropped from 85% coverage to 8%. At this point I found these articles:

  • Multiple threads on this forum saying Singletons are less than ideal

  • In my reading I found guice so I could essentially simulate singletons (I think, at least), but I'm wondering if this:

  • Appropriate
  • Is there a better, more test-friendly solution/design pattern

  • At the end of the day, I just want to learn what I should do in situations like this in the future. What can be done? How does one go about unit testing file I/O operations? What about testing static classes? Singletons?

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    Guice uses dependency injection, which means it's a lot easier to mock out things in your instance.
    It's probably between that and Spring, and I think Guice is a lighter toolkit.

    I would recommend either of them over a Singleton which, as you have seen, are a pain to test.
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