Mockito – Using Spies

Seeing as we are continuing our learning with Mockito, specifically going into spies in Mockito, figured it would be worthwhile to do some research into them. I found this article (https://www.baeldung.com/mockito-spy) from Baeldung by Eugen Paraschiv detailing spy usage and complexities which I found very useful. It begins with a description of spies and then goes into examples of usage.

The first example is used on a real object – a list – which a method is then called upon twice, and then Mockito’s verify is called twice with the same method. This allows for “spying” upon an object, hence the name spies. There is then some detail about the @Spy annotation, stubbing a spy, and then the actual differences between a Mock and a Spy. Chiefly, this difference is that a mock uses the Class of a Type, like a “base-bones shell instance,” while a spy “will wrap an existing instance” and can track it in various ways. This is also followed by a blurb about the NotAMockException from Mockito, which wasn’t immediately necessary for my purposes I don’t think.

Overall, I thought this was a great, useful article. It prepped me for continued learning within Mockito and I felt comfortable understanding it. I think I have a good basic understanding of spies and would be ready to begin using them in testing. They’re a good way to analyze object/method behavior and have useful applications for when a project is only partially written. I look forward to using spies in the future. Most of what I’ve learned within the world of Mockito has been super interesting thus far.

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