Tdd Revisited

TDD Revisited Jon Limjap

MVP for Visual C#

What is TDD? 

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Using unit tests to design software Allows change in code without fear of changing functionality Produces loosely coupled objects and methods with single responsibilities Unit tests are just side effects: main point is DESIGN

What is TDD not? 

Substitute for QA testing

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Necessarily means successful project

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Silver bullet

Mindset

Red 

New code 

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Write test before implementing class Internal workings of classes and methods should not matter

Existing code 

Write test to reproduce bug

Green 

Write least possible code to pass all tests

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Take shortcuts if necessary

Refactor! 

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Applies to both implementation code and 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

Writing tests 

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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 

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

How to test in isolation? 

Stubs 

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Method returns a specified result, e.g., property getter returns a constant value

Mocks 

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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 

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Make sure everything works together Also applies to the file system, web services, etc., ergo, everything that can fail without you knowing

Integration testing sucks because... 

Fragile Tests 

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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)

Demo AAA, Stubs, Mocks, & integration testing using MbUnit and Rhino Mocks 3.5