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Bye Bye Cowboy-Coder 
days!
What do developers do for living? 
Change the code!
Four Reasons to Change Software 
• Adding a feature 
• Fixing a bug 
• Improving the design 
• Optimizing resource usage
Changing Software 
Adding a 
Feature 
Fixing a Bug Refactoring Optimizing 
Structure Changes Changes Changes 
New 
Changes...
Preserving behavior 
Existing Behavior New Behavior
Risky Change 
1. What changes do we have to make? 
2. How will we know that we've done them correctly? 
3. How will we kno...
How?
Working with Feedback! 
Yes, Unit Tests…
Few qualities of Unit Tests 
• They run fast 
• They help us localize problems
Dependencies… 
• No way to run separately 
• Takes time to load 
• Hard to localize problem
GUI Tests 
Integration 
Tests 
Unit Tests
GUI Tests 
Integration 
Tests 
Unit Tests
Lag Time 
Time to fix/Price 
1 Minute 10 Minutes 1 Hour 1 Day 1 Week 
Time to fix/Price
The Legacy Code Dilemma 
When we change code, we should have tests in place. To put 
tests in place, we often have to chan...
The Legacy Code Change Algorithm 
1. Identify change points 
2. Find test points 
3. Break dependencies 
4. Write tests 
5...
Sensing and Separation 
• We break dependencies to sense when we can't access 
values our code computes 
• We break depend...
Faking Collaborators 
• Fake Objects 
• Mock Objects 
• Nothing!
Sprout
Sprout Method 
1. Identify where to change 
2. Wdown a method call and then comment it out. 
3. Determine what local varia...
Sprout Class 
1. Identify where you need to make your code change. 
2. Write class in that place, and call a method; then ...
Wrap
Wrap Method 
1. Identify a method you need to change 
2. If the change can be formulated as a single sequence of 
statemen...
Wrap Class 
1. Identify a method where you need to make a change. 
2. Create a class that accepts the class you are going ...
TDD and Legacy Code 
1. Get the class you want to change under test 
2. Write a failing test case 
3. Get it to compile 
4...
Allways check if tests are testing 
1. Write test and new code in separate changelist 
2. Shelve new code change list 
3. ...
Characterization Tests 
1. Use a piece of code in a test harness 
2. Write an assertion that you know will fail - let the ...
I Can't Get This Class into a Test 
Harness 
• Lean on the Compiler 
• Extract Interface 
• Extract Implementer 
• Subclas...
When All Else Fails, Do Some Scratch 
Refactoring
Questions?
Agile Turas Lietuvoje 
• Agile Tour Kaunas – rugsėjo 25 d. 
• Agile Tour Vilnius – spalio 9 d. 
• Agile Master Classes 
ww...
The World’s Best Intro to TDD 
• J. B. Rainsberger, Kanada 
• 2 Dienų mokymai, Kaune 
• Rugsėjo 23 - 24 d. 
www.agileturas...
Bye Bye Cowboy Coder Days! (Legacy Code & TDD)
Bye Bye Cowboy Coder Days! (Legacy Code & TDD)
Bye Bye Cowboy Coder Days! (Legacy Code & TDD)
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Bye Bye Cowboy Coder Days! (Legacy Code & TDD)

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Bye Bye Cowboy-Coder days! by Vytautas Dagilis.

„Working Effectively with Legacy Code“- one of the best books which talks about Unit testing and TDD. Presentation covers best practices listed in the book as well as shows which of them were successfully implemented in practice. You will find out how to commit changes and be sure that they work even without running and testing application itself.

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Bye Bye Cowboy Coder Days! (Legacy Code & TDD)

  1. 1. Bye Bye Cowboy-Coder days!
  2. 2. What do developers do for living? Change the code!
  3. 3. Four Reasons to Change Software • Adding a feature • Fixing a bug • Improving the design • Optimizing resource usage
  4. 4. Changing Software Adding a Feature Fixing a Bug Refactoring Optimizing Structure Changes Changes Changes New Changes Functionality Functionality Changes Resource Usage Changes
  5. 5. Preserving behavior Existing Behavior New Behavior
  6. 6. Risky Change 1. What changes do we have to make? 2. How will we know that we've done them correctly? 3. How will we know that we haven't broken anything?
  7. 7. How?
  8. 8. Working with Feedback! Yes, Unit Tests…
  9. 9. Few qualities of Unit Tests • They run fast • They help us localize problems
  10. 10. Dependencies… • No way to run separately • Takes time to load • Hard to localize problem
  11. 11. GUI Tests Integration Tests Unit Tests
  12. 12. GUI Tests Integration Tests Unit Tests
  13. 13. Lag Time Time to fix/Price 1 Minute 10 Minutes 1 Hour 1 Day 1 Week Time to fix/Price
  14. 14. The Legacy Code Dilemma When we change code, we should have tests in place. To put tests in place, we often have to change code.
  15. 15. The Legacy Code Change Algorithm 1. Identify change points 2. Find test points 3. Break dependencies 4. Write tests 5. Make changes and refactor
  16. 16. Sensing and Separation • We break dependencies to sense when we can't access values our code computes • We break dependencies to separate when we can't even get a piece of code into a test harness to run
  17. 17. Faking Collaborators • Fake Objects • Mock Objects • Nothing!
  18. 18. Sprout
  19. 19. Sprout Method 1. Identify where to change 2. Wdown a method call and then comment it out. 3. Determine what local variables you need for the call 4. Determine return value 5. Develop the sprout method using test-driven development 6. Remove the comment in the source method
  20. 20. Sprout Class 1. Identify where you need to make your code change. 2. Write class in that place, and call a method; then comment those lines out 3. Determine what local variables you need from the source method, and make them arguments to the classes' constructor 4. Determine return values to the source method and add a call in the source method to receive those values. 5. Develop the sprout class test first 6. Remove the comment in the source
  21. 21. Wrap
  22. 22. Wrap Method 1. Identify a method you need to change 2. If the change can be formulated as a single sequence of statements in one place, develop a new method for it using test-driven development 3. Create another method that calls the new method and the old method
  23. 23. Wrap Class 1. Identify a method where you need to make a change. 2. Create a class that accepts the class you are going to wrap as a constructor argument. 3. Create a method on that class, using test-driven development. 4. Write another method that calls the new method and the old method on the wrapped class 5. Instantiate the wrapper class in your code in the place where you need to enable the new behavior
  24. 24. TDD and Legacy Code 1. Get the class you want to change under test 2. Write a failing test case 3. Get it to compile 4. Make it pass (Try not to change existing code as you do this) 5. Remove duplication 6. Repeat
  25. 25. Allways check if tests are testing 1. Write test and new code in separate changelist 2. Shelve new code change list 3. Ensure tests are failing
  26. 26. Characterization Tests 1. Use a piece of code in a test harness 2. Write an assertion that you know will fail - let the failure tell you what the behavior is 3. Change the test so that it expects the behavior that the code produces 4. Repeat
  27. 27. I Can't Get This Class into a Test Harness • Lean on the Compiler • Extract Interface • Extract Implementer • Subclass and Override Method • Parameterize Constructor • Parameterize Method • Extract and Override Getter • Extract and Override Factory Method • Singleton Design Pattern
  28. 28. When All Else Fails, Do Some Scratch Refactoring
  29. 29. Questions?
  30. 30. Agile Turas Lietuvoje • Agile Tour Kaunas – rugsėjo 25 d. • Agile Tour Vilnius – spalio 9 d. • Agile Master Classes www.agileturas.lt
  31. 31. The World’s Best Intro to TDD • J. B. Rainsberger, Kanada • 2 Dienų mokymai, Kaune • Rugsėjo 23 - 24 d. www.agileturas.lt/master-classes

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