This probably sounds like a dumb question, forgive me if I'm asking this in the wrong place, I'd be happy to delete it if so. I'm sort of new to unit testing and I'd like to learn best practices regarding this question, it's been bugging me for a while.
Assume that there is a method which takes an array as the input and performs some algorithm to its elements. There may be a situation where the method is called repeatedly with input containing elements that have already been processed by the object (and remembered somewhere). I'd like to test that the method doesn't process the same input elements twice, i.e. that it does nothing the second time it encounters those items.
The object under test is actually a wrapper around another object that is provided as a depencency to it, so I can mock that object and verify that the necessary processing methods are called.
So my question is:
How many input elements would you consider to be "enough" to in order to test that the method works properly (for both old and new elements)? One? Three? Ten?