Unit testing is a form of software testing where part of the software is tested and working. Recently I’ve been introduced to some methods of unit testing where a temporary object is created in place of an existing object in order to perform testing. The term for this is “Test Doubles”, as just like an actor in a movie has a double, doubles are created for objects in the program for the purpose of testing them. I’ve learned about different types of test doubles in my Software Quality and Test Assurance course, and I’d like to examine a few and give a brief explanation about how they work. The names of these test doubles are dummies, stubs, fakes, and mocks.
Dummy objects are made for the purpose of allowing methods to call an argument, and therefore they do not have any implementation themselves. These are used for methods are not actually important for your tests. For example, if you are trying to test a method and have it return something specific, then a dummy method can be created instead of making a method with code that isn’t relevant for the test.
Stubs, similar to dummy objects, are created for the use of testing code without needing to fully develop it. A test class is called to the stub, and the stub returns a value that is controlled. This is useful for scenarios where the result of the test changes depending on what the input is.
These test doubles make testing for code easier. They reduce the need of excessive code and allow for the methods in the test class to simply call the these test doubles instead. Each different test double has its own use depending on the objective you are trying to reach with your testing.
This article and blog provided very useful info regarding what each test double does and demonstrated each type of test double with examples.
https://dzone.com/articles/test-doubles-mockito
https://mokacoding.com/blog/swift-test-doubles/#:~:text=Dummy,the%20behaviour%20you%20are%20testing.
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