A Presentation I did at Agile Practitioners 2015 http://apilconf.com/

1. Here’s the codebase

2. About Me
• Clean coder, TDDer, Software Craftsman
• Over 12 years of development
• Lead the infrastructure operations and development
workflows at StartApp
• Tech lead and scrum master (eBay)
egolan74@gmail.com
http://eyalgo.com/
@eyalgo_egolan

3. OOD
Open mind
Attitude over technique
About the Presentation

5. What is Legacy Code?
“…Legacy code refers to an application
system source code that is
no longer supported…” (techopedia)

6. This is Reality
New features…
Modify existing behavior…
Removing features…
Fixing bugs…

7. Working With Legacy Code
Modify behavior of existing
(unfamiliar) code

8. Identify
requirements
Understand
the code
Modify the
code

9. I changed the ‘if’ with a
‘switch’. Is there a new
bug?

11. Why Tests?
Risky change
Refactoring, new feature, bug
Feedback
Assurance and confidence

12. Summing Up
We need to modify code
We want safety using tests

13. Summing Up
We need to modify code
We want safety using tests
The code does not have
tests

14. What is Legacy Code ? (revised)
“Code without tests”
Michael Feathers
(Working Effectively with Legacy Code)

15. What is Legacy Code ? (revised)
“Code without tests”
Michael Feathers
(Working Effectively with Legacy Code)
Untestable code

16. Process
/pro-cess/
def: A number of actions or
functions done in order to
produce a desired result.

17. Identify
requirements
Understand
the code
Write tests
Modify the
code

18. Identify requirements Understand the code
Write tests Modify the code
Working with
Legacy Code

19. Working With Legacy Code (revised)

21. Obstacles
I don’t understand it
I don’t have time
Unstructured code
Breaking dependencies

22. I Don’t Understand the Code
Debugging…

23. I Don’t Understand the Code

24. I Don’t Understand the Code
Extract Methods
Move fields
Create classes
Throw that code away…

25. I Don’t Understand the Code

26. Difficult to Instantiate the Class

27. Difficult to Instantiate the Class
Expose Static Method (which does not use
instance’s variables)
1. Write test that access the method to
be tested
2. Extract the body to a static method
3. Call the static method from the
original one

28. Adapt Complicated Class
Adapter
Test
with
fake

29. Object Creation in the Constructor

30. Object Creation in the Constructor
In your test: create a subclass for testing

31. Static Methods
Test this
Fake this

32. Static Methods
Create a wrapping instance method
Fake this

33. Singleton

34. Singleton
Introduce a setter for ‘instance’

35. Factory Method

36. Factory Method
1
Inject fake server

37. Hidden Method
• Test through a public method
• Extract to a new class
• Expose the method

38. Did I Break Something?
Do one thing at a time
Preserve signature
Trust your computer and IDE
Pair programming

39. Huge Method
• Usually not following SRP
• Usually with too many dependencies
• Invest time and create a safety harness
• Refactor: extract to smaller, tested
methods, extract class

40. More Operations
Introduce / Extract interface
Rename (better understanding)
Expose visibility (package protected)
Extract and override

41. Tools
Use your IDE
mockito
PowerMock and EasyMock
Pair Programming

42. Preliminary Knowledge
OOD
SOLID
Unit testing frameworks
Clean code
Refactoring principles

43. Attitude

44. Ask Yourself
1. What changes do we have to make?
2. How will we know that we’ve done
them correctly?
3. How will we know we haven’t
broken anything?

45. I Don’t Have Time

46. Always leave the place cleaner
than you found it
Boy scouts Rule

48. Q & A
Thank You
egolan74@gmail.com