The perfect pair Chris Ayers Dependency Injection & Unit Testing

Chris Ayers DevOps Lead @ New Signature Linkedin: /in/chris-l-ayers/ Twitter: @Chris_L_Ayers Projects: https://github.com/Codebytes /UnitTestingDemo https://github.com/Codebytes /DependencyInjectionDemo

Topics • Dependency Injection • Why? • SOLID • Design Patterns • Types • Features • DEMO • Unit Testing • Terms • Test Layout and Naming • Mocking • Best Practices • DEMO

Why? • Clarity • Maintainability • Reuseability • Modularity • Testability • Use Different Implementations

SOLID • Single Responsibility Principle • Open/Closed Principle • Liskov Substituion Principle • Interface Segregation Principle • Dependency Inversion Principle

Patterns • Façade • Factory • Strategy • Visitor • Command

Façade Pattern Client -complexFacade Façade +ComplexProcess Subsystem 1 +ComplexStep1 Subsystem 2 +ComplexStep2 Subsystem 3 +ComplexStep3 Subsystem 4 +ComplexStep4

Factory Pattern Client -shapeFactory <> Shape +draw() ShapeFactory +GetShape() : Shape Circle +draw() Square +draw() Triangle +draw() Implements Implements Implements Creates

Strategy Pattern <> CookingMethod +Cook() Dinner -cookingMethod: CookingMethod Microwave +Cook() ToasterOven +Cook() Oven +Cook() Implements Implements Implements Uses

Types of Dependency Injection

No Dependency Injection • Not using interfaces to reduce coupling • Hard to test • No clear understanding of relationships between different classes

Property Injection • Initialization not guaranteed • Can be good for bigger/complex objects

Method Parameter Injection • When a dependency is used for only method and is an edge case

Constructor Injection • Clear understanding of dependencies

Path to Loosely Coupled Classes Tightly Coupled Classes Implement IoC using Factory Pattern Implement DIP by creating Abstractions Implement Dependency Injection Use IoC Container Loosely Coupled Classes

Dependency Injection - Scopes Transient Scoped Singleton

Dependency Injection - Features Composition Root Configuration Scopes Factory Support

Dependency Injection - Frameworks .Net Core Unity Castle Windsor Ninject AutoFac SimpleInjector Spring.NET StructureMap

Dependency Injection - DEMO

Resources DEPENDENCY INJECTION IN ASP.NET CORE - HTTPS://BIT.LY/34UR0IB FRAMEWORK-PROVIDED SERVICES - HTTPS://BIT.LY/355G0YV IDISPOSABLE - HTTPS://BIT.LY/2VSH9SJ

Decoupling is essential for unit testing. DI is a great way to achieve decoupling. Unit Testing

Unit Testing – Terms (SUT) System Under Test or (CUT) Class Under Test Test Doubles Fake Mock Stub Spy Dummy Objects

Unit Testing - Architectures • Easy to Test Code • Inversion of Control (IoC) • Interface Segregation • Functional Programming • Hard to Test code • It is tightly coupled to the concrete implementation. • It violates the Single Responsibility Principle. • It lies about its dependencies. • It is hard to understand and maintain.

Unit Testing - Layout Split up tests by assembly/project. • Ex: if you have two libraries: foo.dll, bar.dll • have 2 unit test assemblies: foo.tests.dll, bar.tests.dll Try to have at least 1 test class per class • Ex: if you have two classes in project foo: a.cs, b.cs • have 2 unit test classes in project foo.tests: aTests.cs, bTests.cs • If there are a lot of methods, or tests for some methods, split it up if there are a too many tests in one class. Use folders to mirror layout and namespaces of target project

Unit Testing - Naming Name test class for the class under test • Foo.cs -> FooTests.cs [UnitOfWork_StateUnderTest_ExpectedBehavior] Examples • public void GetLines_twoLineString_returnsTwoStrings() • public void GetNonWhitespaceLines_null_Throws() • public void ReplaceMultiple_stringWithHashNonMatchingMappings_String() • public void ReplaceMultiple_stringMatchingMappings_UpdatedString()

Unit Testing – Frameworks Nunit Xunit MStest

Mocking – Frameworks Moq NSubstitute JustMock FakeItEasy

Unit Testing – Gotchas Usually only works for Interfaces or Virtual Methods. Statics can be difficult; refactoring can help or Microsoft Fakes Mocking can make assumptions about boundaries

Unit Testing – Best Practices AAA Arrange Act Assert One Assert Per Test Method Avoid Test Interdependence Keep It Short, Sweet, and Visible Recognize Test Setup Pain as a Smell Add Them to the Build

Unit Testing – What is a good test? Fast Isolated Repeatable Self- Checking Timely

Unit Testing - DEMO

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