An Introduction To Test Driven Development

An Introduction to Test Driven Development Jacinto Limjap, Jr. Microsoft Most Valuable Professional – Visual C# Senior Software Design Engineer, Cormant Technologies

Agenda • • • • • • • •

What is TDD? What is TDD not? Arrange, Act, Assert TDD Mindset How to test in isolation? What about the database? Integration tests suck because...

What is TDD? • Using unit tests to design software • Allows change in code without fear of (inadvertently ) changing functionality • Produces loosely coupled objects and methods with single responsibilities

What is TDD? • Unit tests are just side effects: main point is DESIGN • Write tests first, code later (?!) 

What is TDD not? • Substitute for QA testing • Necessarily means successful project • Silver bullet

Writing tests • Think about how you want to express your code and intentions • Think about inputs, and intended output • Separate small, isolated areas of functionality •

Arrange, Act, Assert • Arrange all necessary preconditions and inputs • Act on the object or method under test • Assert that the expected results have occurred •

Mindset

Red • New code – Write test before implementing class/method – Internal workings of classes/methods should not matter

• Existing code – Write test to reproduce bug

Green • Write least possible code to pass all tests • Take shortcuts if necessary

Refactor! • Applies to both implementation code and unit test code • Change code without changing functionality (ergo, without introducing bugs) • Remove implementation shortcuts – make sure software design is sound/follows tenets of OOP • Optimize for design/performance/maintainability

•

Rinse and Repeat! 

How to test in isolation? • Classes and methods should have single responsibility(!!!) • Loose coupling •

How to test in isolation? • Stubs – Method returns a specified result, e.g., property getter returns a constant value

• Mocks – Asserting that a certain method has been called within a test – Test checks for the method call, not the result, but some tests check for both 

What about the DB? • Integration tests – Makes sure everything works together – Also applies to the file system, web services, etc... – Handles everything that can fail without your absolute control 

Integration testing sucks because... • Fragile Tests – Depends on state of external system – Breakage cause lost confidence on tests – even if it's not the tests' fault

• Usually leaves artifacts behind (files, orphaned DB data) 

Question and Answer Blog and email: http://dotnet.kapenilattex.com [email protected] 



Programming/IT questions can be posted at: http://nullpointer.ph

