Legacy code workshop at [XP Day Vietnam 2015] Speaker: Stanly Lau Homepage: http://xpday.vn

1. www.odd-e.com
Fight Legacy Code!
Write Unit Test!
Stanly Lau

2. 2
I’m Stanly
• Lives in Singapore!
• Agile coach, SW developer!
• Worked in small to large
companies!
• Experienced in Insurance, Mobile
Safety, Education, Logistics and
Banking!
• Java, .Net, JavaScript, Objective-C
stanly@odd-e.com

5. 5
What is Legacy Code?!
!
The Problem!
!
How to deal with it?

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7. What is legacy code?
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8. Legacy Code is!
Code without Unit Test
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Michael Feathers

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It is not a unit test when:
• It talks to the database!
• It communicates across the network!
• It touches the file system!
• It can't run at the same time
as any of your other unit tests!
• You have to do special things to your
environment (such as editing config
files) to run it.
Michael Feathers

10. The problem
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Inheritance nightmare

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Code tends to grow

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amount of bad
code
panic
amount of code
smells
time spend on
bug fixing
motivation
developers
quick hacks
opportunity for
# of bugs
indicates
O
refactoring
O

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Existing Behaviour New
This is where we spent most time on,!
preserving behaviour!
Codebase

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Productive
Working duration in a day
Does your day
looks like this?

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Productive =(
Don’t know why the ‘if’
doesn’t work

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Productive =(
Stuck on
understanding what the
code is doing

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Productive =(
Stuck on thinking of a
general solution to solve multiple
problems

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Productive =(
Realised you misunderstood
the requirements

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Productive
=(
Fixing production bug

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Features
Estimates
Business Developers
Competitive dynamic
Limits everyone’s
perspectives

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James Grenning
“Software change is part of being a
developer, so you better get used to it. !
Even more, you better get good at it!”

23. How to deal with it?
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Modern engineering practices
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Test-Driven
Development
Refactoring
Continuous
Integration
Emergent Design

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Test-driven development
•Increments of functionality!
•Always in working state
Code and fix
•Large functionalities!
•Long time to get to a working statef
t

26. The Legacy Code Dilemma
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When we change code, we should have tests in place. To put tests in
place, we often have to change code.

27. But I don't understand the code
well enough to change It =(
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Scratch Refactoring
Notes/Sketching
Delete Unused Code

28. Legacy code algorithm
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1. Identify change point!
2. Find test points!
3. Break dependencies!
4. Write tests!
5. Make changes and refactor

29. Exercise:!
Dependency Breaking!
Characterisation Tests!
!
http://bit.ly/FightLegacyCode
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30. Are we going faster?
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Feels faster
Feels slower

31. 35
Kent Beck
“I'm not a great programmer;!
I'm just a good programmer with great
habits”

32. Closing
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33. Books - Technical Practices
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34. 38
@avernois

35. stanly@odd-e.com
!
@stanlylau
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