Just as we encourage tests of smaller size, at Google, we also encourage engineers to write tests of narrower scope. As a very rough guideline, we tend to aim to have a mix of around 80% of our tests being narrow-scoped unit tests that validate the majority of our business logic; 15% medium-scoped integration tests that validate the interactions between two or more components; and 5% end-to-end tests that validate the entire system.
