Distinguish between Mocks and Fakes inside tests

### Description

Hello,

in the `test` section, there is no differentiation between `Mocks` and `Fakes`. The word `Mock` is used for both `Fakes`(Implementation of classes) and `Mocks`(abstract classes).

- Mocks should only be abstract classes, which should be mockable in tests and don`t have implemented methods.

- Fakes should be minimal working implementation of classes.

In the `mockito` package are [some samples](https://pub.dev/packages/mockito#mocking-a-function-type) for `Mocks` and `Fakes`