What does it really mean to test an interface not the implementation?
let's say there is a Shape interface.
interface IShape { double Area(); }
A Rectangle class and a Triangle class implement it. Now should i write tests for:
- IShape interface and test both implementations in a single test file?
- Write tests for Rectangle and Triangle class separately, testing their implementation of Area() ?
- Do something else?
From what I see I am testing implementations either ways. How do you even test an interface without testing the implementation? Can someone please help clarify my doubts? Thanks!
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That advice does not literally refer to
interfacethe programming language feature. It means to test the observable behavior of a component, not internal implementation details.In your example, write tests for both Rectangle and Triangle that call
area, and assert the result is correct. But do not test, for example, the order of mathematical operations that were run to calculate the result. The details of the math are an internal detail, not part of the "interface".Fuck! Now it makes sense to me. I thought it literally meant an interface. Thanks a lot for clarifying!
No problem! I thought there was a good chance you already know the concept, just not in the exact, unfortunately-overloaded words of your post title.