Dependency Injection Example

This repository contains a simple test project to showcase conventions for injecting mocked dependencies to allow real unit testing.

Why

• If a class AService just uses BService, in our unit tests of AService will be code of BService be executed.
• Changes of the implementation in BService can change test results of AService.
• To avoid this, we inject a mock of BService when testing AService

Conventions

Services

• Inject dependency in initializer, with an default parameter if possible. This default value can also be provided by a factory class in the future.

ServiceProtocols

• Always name it with Protocol as suffix
• Put the protocol in a separate file in the same folder as the Service
• Always create protocols, to allow dependent classes to quickly mock it. Only create mocks of your class if needed

ServiceMocks

• Mocks have to be classes to be injected and changed from outside, namely our test functions.
• Mocks should be placed in the test target
• Mocks must have Mock as suffix.
• Always Put mock variables directly above the specific function.
• Name those variables alwasys beginning with the function name

Tests

• Name the tested class variable sut (system under test)
• Name functions like this func testFunctionName_input_expectedOutput()