Pair Programming

XP Rule of Thumb

“When something is difficult or painful, do it more often until it becomes easier.”

Roles

•Driver▫Controls mouse and keyboard

•Navigator/Observer▫Actively reads and reviews code while it is

being written▫Thinks about the bigger picture▫Provides strategic direction▫Help ensure quality and minimise defects

•Switch frequently

Rules• All production code must be developed by a pair

▫Conversely, this means that are plenty of other activities that you can undertake in the absence of a pair.

• It's not one person doing all the work and another watching▫Keyboard should be moving back and forth between

the two participants several times an hour• Don’t pair for more than 75% of the day• Switch pairs frequently

▫At least daily

Guidelines

Start with a defined task

•The task should be something you are confident that you can complete in an hour or two

Agree on one tiny goal at a time

•Something you can complete in minutes•Ping pong with red, green, refactor works

well

Talk lots!• When people are pairing well, they are

talking back and forth almost non-stop. • Stating the problem in words to another

person helps focus your mind and helps engage your partner's mind. It also ensures that you both know what you are working on right now.

• Here are some common things to say while pairing:▫ Do you think this is a valid test?▫ Does that look correct to you?▫ What’s next?▫ Trust me (when writing code to illustrate

your point rather than trying to explain)

Rely on and support your partner• Driver

▫Complete current goal (tiny task) as quickly as possible

▫Trust the observer to notice larger issues• Observer

▫Pay attention▫Think about possible bugs, larger issues, and ways

to simplify or improve the design.▫Bring up errors and code that you find unreadable

right away.▫Bring up larger issues and ideas for design

improvement after the driver is done.▫ Jot later tasks down so that driver can stay focused.

Sync frequently

•It is normal to get out of sync▫Be unsure of what your partner is doing▫Be unclear on the current (tiny) task

•When it happens, TALK and sync up again

Celebrate

•Celebrate completed tasks and overcome problems, e.g.▫High five when a test passes ▫High five when you write failing test

Switch roles often

•At least every half an hour

Red, Green, Refactor

Suggested:

1. Driver writes failing test2. Switch roles3. New driver writes code

to help test pass4. Chat about what can be

refactored and make changes together

5. Driver writes next failing test

6. Switch roles 7. Loop