Test Driven Development

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Session Code: NE.17 Introduction in the TDD Mantra Dennis van der Stelt

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Transcript of Test Driven Development

  • 1. Dennis van der SteltIntroduction in the TDD Mantra Session Code: NE.17

2. Introduction Class-A Kennisprovider Microsoft development Training / Coaching www.class-a.nl Dennis van der Stelt Trainer / Coach Weblog at http://bloggingabout.net/blogs/dennis/ 3. Agenda A quick introduction into unit testing Test Driven Development mantra Refactoring Benefits of Test Driven Development Demo Key rules of Test Driven Development Mocking / Stubbing Legacy code 4. A quick introduction Unit testing 1. Automated testing 2. Facilitates change 3. Simplifies integration 4. Documentation 5. unit testing isnt about just testing code its about allowing you to determine when behavior changes 6. TDD Mantra REDGREEN IM TEST-DRIVEN Write the test Write the code Refactor RepeatREFACTOR 7. TDD Mantra Where to begin? Work from specification (or notes, or napkin) Create a list of tests Pick the simplest one Make test, make code Refactor Find a bug? Create the test that wouldve caught it! 8. Test Driven Development ...is not about testing. Its about design Its about unambigious requirements Its also about simplicity and YAGNI Simplicity is more complicated then you think. But its well worth it. Ron Jeffries, Extreme Programming Installed, 2001 9. Test Driven Development ...is about simple design that 1. 2. 3. 4.Runs all tests Reveals all intention Has no duplication Has the fewest number of classes and methods 10. Test Driven Development The act of writing a unit test is more an act of design then of verification- Robert C. Martin Test-driven development seeks specification, not validation, letting you think through your design before you write your functional code- Scott Ambler Test-Driven Development is a powerful way to produce well designed code with fewer defects- Martin Fowler Fewer defects, less debugging, more confidence, better design, and higher productivity in my programming practice- Kent Beck 11. Benefits of TDD (1/3) Benefits on your design & code Exposes design flaws & invalid assumptions Simpler class hierarchies Less code, smaller functions Less conditional code Faster development time Tests are both design & documentation 12. Benefits of TDD (2/3) Benefits on your tests & bugs Tests cover *everything* Bugs found earlier & faster Bugs reproduced more easily Less (difficult) debugging 13. Benefits of TDD (3/3) Cost of changeTest-Driven Development embraces change! Waterfall 14. Cons of TDD Needs practice, but youll learn to love it! Needs discipline Need to know OODP Scares away managers 15. Bowling game First a quick design session 16. Bowling game 0 4 42 4 104 3 174 + (2+4) 6 303 2 35559 650 0 659 0 747 2 8317 + (6+4+3) 35 + (10+9+1) + 1 + 0) 55 + (910 frames, each holds 2 throws Spare: 10 pins 2nd try, next throw added extra Strike: 10 pins in 1st try, score next frame added 10th frame spare or strike, player can make extra balls to complete frame. 17. Quick design sessions next frameFrameGame +roll(pins : int) +score() : intThe score for spare or strike depends on the frames succesor10+score() : intRoll 1..2-pins : int1We clearlyfunction must A game has ten frames. A frame has 1 or 2 roles. The score need the Game class. iterate through all the frames, and calculate all their scores. tenth frameThe tenth frame has two or three roles. It is different from all the other frames. 18. Bowling game Finally some code! 19. Key rules of TDD A test is no unit test if it talks to a database it communicates across the network it touches the file system it cant run at the same time as other tests you have to perform actions to run the tests (ex. configuration change) 20. How to isolate your code 21. How to isolate your codedatabaselogging serviceremote server 22. How to isolate your code 23. Mocks & Stubs A mock or stub is a stunt double for an object outside your unit an external object (database) a complex object(s) a not yet developed objectMocking & Stubbing are different things! 24. Isolation framework [TestMethod] public void Does_AllowDependencyInjection_When_CreatingInstance() { // Arrange var fake = Isolate.Fake.Instance(); Customer cust = new Customer(); // Act BusinessAction ba = new BusinessAction(fake); ba.PerformSomeSortOfAction(cust);// Assert Isolate.Verify. WasCalledWithExactArguments(() => fake.SaveChanges(cust)); } 25. Legacy code What is legacy code? Wikipedia : Legacy code is source code that relates to a no-longer supported or manufactured operating system or other computer system.Why is legacy code bad? The previous developer isnt there to explain it. It takes time to learn the code. Its not easy to change the code. You might break some part of the application you didnt even touch. 26. Legacy code Now imagine... Without a tests, Youre developer on unitproject, What if you have unit tests? as we speak! youre writing legacy code You get sick for two weeks, Yourhave tests to explain the code You code needs to be completed, Another developer comes in. You have tests to learn the code Michael Feathers Working Effectively with Legacy CodeYou have tests to verify what you did works, and did not break any other part of the application.- The previous developer isnt there to explain it. - It takes time to learn the code. - Its not easy to change the code. - You might break some part of the application you didnt even touch. 27. Conclusion:WRITE UNIT TESTS! and do it the right way using Test-Driven Development. 28. Thank you for your attention Dennis van der Stelt [email protected] http://twitter.com/dvdstelt/ http://bloggingabout.net/blogs/dennis/ Resources to more information can be found here, incl. this slidedeck. 29. Evaluation form Vul je evaluatieformulier in en maak kans op een van de prachtige prijzen!! Fill out your evaluation form and win one of the great prizes!!Session Code: NE.17