CppCon 2018

Callbacks are a commonly used technique for delivering data and passing control from one component to another. Their many uses include handling asynchronous events, providing customizations, and (with polymorphic lambdas) enable functional-style programming in C++. Testing components which invoke polymorphic callbacks can be a challenge, and this leads some developers to either avoid testing altogether, or to rely on mocking frameworks such as Google Mock.

Mocking frameworks sometimes rely on a Domain Specific Language or other syntax for expressing expectations on the mocked objects. My intention for this talk is to outline some ways in which standard C++ features and idioms can be used to test components with callbacks, as an alternative to such frameworks. In particular, I'll show how employing core features - lambdas, std::function, and RAII - allows us to build mocks which clearly express the desired behavior from the code under test, whilst being expressive and hard to misuse.