Mud Tires: Getting Traction in Legacy Code

MUD TIRES: GETTING TRACTION IN LEGACY CODE

Cory FoySenior ConsultantNet Objectives

@cory_foy

cory.foy@netobjectives.com

http://blog.coryfoy.com

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WHAT IS LEGACY CODE?

• Code we’ve gotten from somewhere else

• Code we have to change, but don’t understand

• Demoralizing Code (Big Ball of Mud)

• Code without automated unit tests

• Any code older than about 2 hours

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Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Removing Duplication

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Prefactoring

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Prefactoring Refactoring

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Remodeling

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Remodeling

Coding

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Approaches

Strategies

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Strategies

Acceptance Test-Driven Development

Test-Driven Development

Pair Programming

Characterization Tests

Naked CRC

Tell the StoryRefactoring

Sensing Variables

Strategies

Acceptance Test-Driven Development

Test-Driven Development

Pair Programming

Naked CRC

Tell the StoryRefactoring

Sensing Variables

Strategies

Acceptance Test-Driven DevelopmentTest-Driven Development

Pair ProgrammingCharacterization Tests

Naked CRCTell the Story

Refactoring

Sensing Variables

Making Changes

Increasing Confidence

Gaining Understanding

http://www.flickr.com/photos/ransomtech/5811447011

Tell the StoryNaked CRC

Tell the Story

Naked CRC

http://www.flickr.com/photos/west_point/5863829218

Increasing Confidence

Sensing VariablesCharacterization Tests

Pair Programming

http://www.artima.com/weblogs/viewpost.jsp?thread=170799

Sensing Variables

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You need to

Change

ATDDTDD

Refactoring

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Remodeling

Coding

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Remodeling

Coding

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Remodeling

Coding

ATDDTDD

Adding Behavior

Preparing to Add

Behavior

Adding Behavior

Cleaning Technical

Remodeling

Coding

ATDDTDD

Refactoring

Example: Acceptance TDD Basic Employee CompensationEach week, hourly employees are paid • A standard wage per hour for the first 40 hours worked• 1.5 times their wage for each hour after the first 40 hours• 2 times their wage for each hour worked on Sundays and holidays

Example: Acceptance TDD

Standard Hours

Hol/Sun Hours

Wage Pay()

40 0 20

45 0 20

48 8 20

Basic Employee CompensationEach week, hourly employees are paid • A standard wage per hour for the first 40 hours worked• 1.5 times their wage for each hour after the first 40 hours• 2 times their wage for each hour worked on Sundays and holidays

Payroll.Fixtures.WeeklyCompensation

Example: Acceptance TDD

Standard Hours

Hol/Sun Hours

Wage Pay()

40 0 20 $800

45 0 20 $950

48 8 20 $1520

Basic Employee CompensationEach week, hourly employees are paid • A standard wage per hour for the first 40 hours worked• 1.5 times their wage for each hour after the first 40 hours• 2 times their wage for each hour worked on Sundays and holidays

Payroll.Fixtures.WeeklyCompensation

http://www.fitnesse.org

A test is not a unit test if:

- 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.

http://vinkamat.com/2011/tdd-unit-testing-and-benefits/

Refactor

(Refactoring is a) disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior

http://www.flickr.com/photos/phluke/62175794

Feather’s ApproachATDD Approach

Edit and Pray

Feather’s Approach

Identify Change Points

Find Test Points

Break Dependencie

Find Test Points

Break Dependencie

Write Tests

Find Test Points

Break Dependencie

Write Tests

Make Changes

Find Test Points

Break Dependencie

Write Tests

Make Changes

Refactor

ATDD Approach

WriteAcceptance

ATDD Approach

WriteAcceptance

Tests WriteCharacterization

ATDD Approach

WriteAcceptance

ImplementBehavior

ATDD Approach

WriteAcceptance

ImplementBehavior

Get All Tests to Pass

ATDD Approach

WriteAcceptance

ImplementBehavior

Celebrate!

ATDD Approach

WriteAcceptance

ImplementBehavior

Celebrate!

ATDD Approach

WriteAcceptance

ImplementBehavior

Celebrate!

ATDD Approach

WriteAcceptance

ImplementBehavior

Celebrate!

ATDD Approach

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References

Cory Foyfoyc@coryfoy.com@cory_foycory.foy@netobjectives.com

Mud Tires: Getting Traction in Legacy Code

Technology

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