Test Driven Development

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Test Driven Development

  1. 1. Test Driven Development Dhaval Dalal software-artisan.com @softwareartisan
  2. 2. What TDD is not? TDD is not about Testing! TDD is not Test Last or DDT (Design Driven Tests)
  3. 3. What TDD is? TDD or Test First is about evolving the design of the system through Tests.
  4. 4. 2 4 3 2 4 5 TDD Episode
  5. 5. [TestFixture] public class OddNumberFilterTest { [Test] public void FiltersOutOddNumbers() { OddNumberFilter filter = new OddNumberFilter(); int [] numbers = new int [] { 3, 4 }; int [] evenNumbers = filter.Filter(numbers); Assert.That(evenNumbers, Has.Count(1)); Assert.That(evenNumbers, Has.Member(4)); Assert.That(evenNumbers, Has.No.Member(3)); } } dhaval.dalal@software-artisan.com Specify What Software Should Do... Then When Given
  6. 6. public class OddNumberFilter { public int [] Filter (params int [] numbers) { throw new NotImplementedException(); } } dhaval.dalal@software-artisan.com Write Just Enough Code To Compile
  7. 7. Red dhaval.dalal@software-artisan.com
  8. 8. public class OddNumberFilter { public int [] Filter (params int [] numbers) { List<int> evenNumbers = new List<int>(); foreach (int number in numbers) { if (number % 2 == 0) { evenNumbers.Add(number); } } return evenNumbers.ToArray(); } } dhaval.dalal@software-artisan.com Write Enough Code To Pass The Specification...
  9. 9. Green dhaval.dalal@software-artisan.com
  10. 10. dhaval.dalal@software-artisan.com General Test Structure Setup the Givens (Context in which the Test runs) Then verify the Assertions (State or Behavior verifications) Exercise the Whens (Perform the actual operation) Arrange Assert Act
  11. 11. [TestFixture] public class NumberFilterTest { [Test] public void FiltersOddNumbers() { OddNumberFilter filter = new OddNumberFilter(); int [] numbers = new int [] { 3, 4 }; int [] evenNumbers = filter.Filter(numbers); Assert.That(evenNumbers, Has.Count(1)); Assert.That(evenNumbers, Has.Member(4)); Assert.That(evenNumbers, Has.No.Member(3)); } dhaval.dalal@software-artisan.com Add New Feature: Filter-out Non-Primes
  12. 12. [TestFixture] public class NumberFilterTest { [Test] public void FiltersOddNumbers() { OddNumberFilter filter = new OddNumberFilter(); int [] numbers = new int [] { 3, 4 }; int [] evenNumbers = filter.Filter(numbers); Assert.That(evenNumbers, Has.Count(1)); Assert.That(evenNumbers, Has.Member(4)); Assert.That(evenNumbers, Has.No.Member(3)); } [Test] public void FiltersNonPrimes() { NonPrimesFilter filter = new NonPrimesFilter(); int [] numbers = new int [] { 4, 5 }; int [] primeNumbers = filter.Filter(numbers); Assert.That(primeNumbers, Has.Count(1)); Assert.That(primeNumbers, Has.Member(5)); Assert.That(primeNumbers, Has.No.Member(4)); } } dhaval.dalal@software-artisan.com Add New Feature: Filter-out Non-Primes
  13. 13. [TestFixture] public class NumberFilterTest { [Test] public void FiltersOddNumbers() { OddNumberFilter filter = new OddNumberFilter(); int [] numbers = new int [] { 3, 4 }; int [] evenNumbers = filter.Filter(numbers); Assert.That(evenNumbers, Has.Count(1)); Assert.That(evenNumbers, Has.Member(4)); Assert.That(evenNumbers, Has.No.Member(3)); } [Test] public void FiltersNonPrimes() { NonPrimesFilter filter = new NonPrimesFilter(); int [] numbers = new int [] { 4, 5 }; int [] primeNumbers = filter.Filter(numbers); Assert.That(primeNumbers, Has.Count(1)); Assert.That(primeNumbers, Has.Member(5)); Assert.That(primeNumbers, Has.No.Member(4)); } } dhaval.dalal@software-artisan.com Add New Feature: Filter-out Non-Primes Duplication of Concept
  14. 14. [TestFixture] public class NumberFilterTest { [Test] public void FiltersOddNumbers() { OddNumberFilter filter = new OddNumberFilter(); int [] numbers = new int [] { 3, 4 }; int [] evenNumbers = filter.Filter(numbers); Assert.That(evenNumbers, Has.Count(1)); Assert.That(evenNumbers, Has.Member(4)); Assert.That(evenNumbers, Has.No.Member(3)); } [Test] public void FiltersNonPrimes() { NonPrimesFilter filter = new NonPrimesFilter(); int [] numbers = new int [] { 4, 5 }; int [] primeNumbers = filter.Filter(numbers); Assert.That(primeNumbers, Has.Count(1)); Assert.That(primeNumbers, Has.Member(5)); Assert.That(primeNumbers, Has.No.Member(4)); } } dhaval.dalal@software-artisan.com Add New Feature: Filter-out Non-Primes Duplication of Concept Duplication of Concept
  15. 15. Refactor dhaval.dalal@software-artisan.com
  16. 16. public interface IFilter { int [] filter.Filter(param int [] numbers); } dhaval.dalal@software-artisan.com Introduce Abstraction
  17. 17. [TestFixture] public class NumberFilterTest { [Test] public void FiltersOutOddNumbers() { IFilter filter = new OddNumberFilter(); int [] numbers = new int [] { 3, 4 }; int [] evenNumbers = filter.Filter(numbers); Assert.That(evenNumbers, Has.Count(1)); Assert.That(evenNumbers, Has.Member(4)); Assert.That(evenNumbers, Has.No.Member(3)); } [Test] public void FiltersOutNonPrimes() { IFilter filter = new NonPrimesFilter(); int [] numbers = new int [] { 4, 5 }; int [] primeNumbers = filter.Filter(numbers); Assert.That(primeNumbers, Has.Count(1)); Assert.That(primeNumbers, Has.Member(5)); Assert.That(primeNumbers, Has.No.Member(4)); } } dhaval.dalal@software-artisan.com Refactored Code
  18. 18. Red TDD Rhythm
  19. 19. Red Green TDD Rhythm
  20. 20. Red Green TDD Rhythm Refactor
  21. 21. dhaval.dalal@software-artisan.com TDD Rhythm Flowchart Write just enough Code to compile Refactor Code Pass the Test (GREEN) Fail the Test (RED) Write just enough Code to pass the test Specify what the software should do Pass the Test (GREEN)
  22. 22. So, TDD is about… Analyzing what little you actually need to do and how cleanly you can do it! Carving design of your code a unit test at a time.
  23. 23. dhaval.dalal@software-artisan.com Write Tests Before Writing Code ! Focuses the mind (and the development process) " Deliver only what is absolutely necessary. " System so developed does exactly what it needs to do and no more. " Need not code for future ! YAGNI (You Ain’t Gonna Need It!)...no gold plating!
  24. 24. dhaval.dalal@software-artisan.com TDD is a Design Technique ! Makes you think in terms of Object behavior. " How client is going to interact with the object. ! Outside-In ! Object so created is “consumer aware” " What Object provides and needs from environment. " Traditional OOD focuses only on Object’s Implementation ! Inside-Out
  25. 25. dhaval.dalal@software-artisan.com TDD results in a Decoupled Design ! Favors Composition over Inheritance. " Relies on dependency injection for collaborators. ! Avoids tight coupling to global objects " Singletons mix static and state. " Makes design untestable. ! Many small, loosely coupled classes. ! Makes you think of inter-object interactions in terms of interfaces. " Promotes Programming to Super-Types and not Concretes.
  26. 26. Listening to the Tests ! A difficulty in implementing a new feature is usually a symptom that the design can be improved. " Ask why is it difficult to test? Don’t just think how do I test this? ! TDD is not just about functionality, it gives us feedback on code’s internal quality. " How is the coupling and cohesion? " Are we preserving encapsulation? " What about implicit or explicit dependencies? Source: Growing Object-Oriented Software, Guided by Tests
  27. 27. Listening to the Tests ! Check continuously, observe and meditate on the tests, they might tell you something. ! The idea is to let the test drive the design. That’s why it is called Test Driven Design. Source: Growing Object-Oriented Software, Guided by Tests
  28. 28. dhaval.dalal@software-artisan.com Benefits of TDD ! Test-a-little and build-a-little gives confidence " Green bar gives you confidence " Reduces fear of change ! Documentation " Provides starting point to understand code functionality ! Safety Net " Checks Regression " Supports Refactoring
  29. 29. dhaval.dalal@software-artisan.com Benefits of TDD ! Effort " Reduces effort to final delivery " Writing tests is more productive ! Predictable " Tells me when am I done " Continuous Success Vs Illusive Success ! Immediate Feedback " Makes failures shine at you
  30. 30. dhaval.dalal@software-artisan.com Costs of TDD Claim: It is too much work to write tests! Rebut: I’d say “are you looking to create a speculative design?”, “do you want to sleep with a debugger?” Claim: Tests themselves are code, we need to maintain them, that’s overhead! Rebut: I’d say “do you prefer maintaining a big bug list?” Claim: I have to spend time re-orient my thinking! Rebut: I’d say “Just as with any skill, you need to allow some time to apply this effectively.”
  31. 31. Writing Good Tests
  32. 32. dhaval.dalal@software-artisan.com Better Test Practices ! Tests must be Small. " Easy to understand " They do not break when other parts of the code are changed. " One behavioral-assert per test. ! Tests must be Expressive. " Test code should communicate its intent. " It should not take more than 2 minutes for readers to understand what is going on. ! Tests must be Maintainable. " When a test breaks, what it contains should be easiest to fix.
  33. 33. dhaval.dalal@software-artisan.com Better Test Practices ! Tests must execute Fast. " Slow running tests increase Build Viscosity. ! Tests are Specifications, not Verifications. " Do not verify whether the code does what its supposed to do correctly. " Specify what should the code do to function correctly. ! Tests should talk the Domain Language. " Communicate the behavior under test and not how the system implements that behavior. " Improves Communication with Non-Technical Members on the team. " Developers can understand domain faster.
  34. 34. dhaval.dalal@software-artisan.com Better Test Practices ! Tests must run at will. " Able to write and execute tests without worrying about how to execute them. ! Tests must be Isolated " Very little set-up and minimum collaborators. ! Tests must be Thorough " Test all behavior, not methods.
  35. 35. dhaval.dalal@software-artisan.com Better Test Practices ! Tests must be Automated. " Write them such that methods on objects are invoked by code rather than by hand. ! Tests must be Self-Verifiable. " Setup test expectations and compare outcome with expectations for verdicts. ! Tests must be Repeatable. " Executing the same test several times under the same conditions must yield same results.
  36. 36. dhaval.dalal@software-artisan.com JUnit/NUnit Better Test Practices ! Test anything that could possibly break. ! Make testing exceptional scenarios easy to read. ! Always explain failure reason in Assert calls. ! Test should usually improve the design of the code. ! For JUnit Tests " Make Test code reside in same packages, but different directories. ! For NUnit Tests " Make Test code reside in separate project from source project, in same namespace.
  37. 37. dhaval.dalal@software-artisan.com Flavors of Tests ! Object Tests (Unit or Programmer Tests) " Tests behavior of single object at a time. ! Integration Tests " Tests collaboration of a number of objects (how they talk to each other) " Complex fixtures " More brittle ! End-to-End Tests " Thoroughly test the entire system from end-to-end.
  38. 38. dhaval.dalal@software-artisan.com Unit Testing Frameworks ! xUnit framework for Unit Testing " JUnit/TestNG for Java " NUnit/MbUnit for C# " cppUnit for C++ " pyUnit for Python " …and tons of more Unit Testing frameworks.
  39. 39. Thank you dhaval.dalal@software-artisan.com software-artisan.com
  40. 40. dhaval.dalal@software-artisan.com References ! JUnit Recipes " J. B. Rainsberger ! JUnit In Action " Vincent Massol ! Agile Java " Jeff Langr ! Test-Driven Development Rhythm " Gunjan Doshi ! Agile Principles, Patterns, and Practices in C# " Robert C. Martin, Micah Martin ! xUnit Test Patterns " Gerard Meszaros ! On TDD (InfoQ): How Do We Know When We’re Done? " Steve Freeman ! Growing Object-Oriented Software, Guided by Tests " Steve Freeman and Nat Pryce ! 10-Ways-to-Better-Code (InfoQ) " Neal Ford ! Refactoring Away Duplicated Logic Creates a Domain Specific Embedded Language for Testing " Nat Pryce ! Jay Field’s Blog Entry " http://blog.jayfields.com/ 2007/06/testing-inline-setup.html

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