Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Test Your Legacy Code
Search
Noel Rappin
November 07, 2011
Technology
3
210
Test Your Legacy Code
Presented at RubyMidwest, November 2011
Noel Rappin
November 07, 2011
Tweet
Share
More Decks by Noel Rappin
See All by Noel Rappin
Rails on Ruby: How Ruby Makes Rails Great
noelrap
0
350
In Defense of Metaprogramming
noelrap
0
470
Rails 7 Front End Tooling
noelrap
1
580
More Engineers, More Problems: Solutions for Big Teams
noelrap
0
210
The Rails 6 Front End: Building with Webpacker and Stimulus
noelrap
3
1.2k
The Developer's Toolkit
noelrap
0
180
High Cost Tests and High Value Tests: GOTO Chicago 2018
noelrap
2
150
High Cost Tests and High Value Tests
noelrap
1
180
The Road To Legacy is Paved With Good Intentions
noelrap
1
180
Other Decks in Technology
See All in Technology
「良さそう」と「とても良い」の間には 「良さそうだがホンマか」がたくさんある / 2025.07.01 LLM品質Night
smiyawaki0820
1
430
CursorによるPMO業務の代替 / Automating PMO Tasks with Cursor
motoyoshi_kakaku
2
750
Claude Code Actionを使ったコード品質改善の取り組み
potix2
PRO
6
2.6k
2025-06-26 GitHub CopilotとAI駆動開発:実践と導入のリアル
fl_kawachi
1
220
AIとともに進化するエンジニアリング / Engineering-Evolving-with-AI_final.pdf
lycorptech_jp
PRO
0
140
AWS テクニカルサポートとエンドカスタマーの中間地点から見えるより良いサポートの活用方法
kazzpapa3
2
580
KubeCon + CloudNativeCon Japan 2025 Recap
ren510dev
1
300
Beyond Kaniko: Navigating Unprivileged Container Image Creation
f30
0
100
生成AIで小説を書くためにプロンプトの制約や原則について学ぶ / prompt-engineering-for-ai-fiction
nwiizo
4
3.3k
2025-06-26_Lightning_Talk_for_Lightning_Talks
_hashimo2
2
110
無意味な開発生産性の議論から抜け出すための予兆検知とお金とAI
i35_267
0
650
高速なプロダクト開発を実現、創業期から掲げるエンタープライズアーキテクチャ
kawauso
1
140
Featured
See All Featured
Measuring & Analyzing Core Web Vitals
bluesmoon
7
500
Mobile First: as difficult as doing things right
swwweet
223
9.7k
[Rails World 2023 - Day 1 Closing Keynote] - The Magic of Rails
eileencodes
35
2.4k
Building a Modern Day E-commerce SEO Strategy
aleyda
42
7.4k
What’s in a name? Adding method to the madness
productmarketing
PRO
23
3.5k
Build your cross-platform service in a week with App Engine
jlugia
231
18k
The Invisible Side of Design
smashingmag
300
51k
The Web Performance Landscape in 2024 [PerfNow 2024]
tammyeverts
8
680
Faster Mobile Websites
deanohume
307
31k
CoffeeScript is Beautiful & I Never Want to Write Plain JavaScript Again
sstephenson
161
15k
実際に使うSQLの書き方 徹底解説 / pgcon21j-tutorial
soudai
PRO
181
53k
Connecting the Dots Between Site Speed, User Experience & Your Business [WebExpo 2025]
tammyeverts
5
230
Transcript
Test Your Legacy Code Noel Rappin @noelrap Monday, November 7,
11
You are handed a “rescue” project Monday, November 7, 11
Oh. My. God. The last person to work on this
was an idiot Monday, November 7, 11
Now what? Monday, November 7, 11
Shake your fists at the heavens for one minute. Photo
by Sha Sha Chu http://www.flickr.com/photos/shashachu/88654315/ Monday, November 7, 11
Get back to work. Monday, November 7, 11
What is a legacy application? Monday, November 7, 11
Code without tests Monday, November 7, 11
Code based on lost requirements Monday, November 7, 11
You don’t know what “correct” means Monday, November 7, 11
What’s your goal? Monday, November 7, 11
Respect working code. Do no harm. Monday, November 7, 11
Deliver features Monday, November 7, 11
At a sustainable pace Monday, November 7, 11
Improve code quality Monday, November 7, 11
The Boy Scout Rule Monday, November 7, 11
Our rescue project needs to change Monday, November 7, 11
Goofus and Gallant Monday, November 7, 11
“First, let’s write tests and cover the whole app” Monday,
November 7, 11
“That change is easy, I’ll just drop that in” Monday,
November 7, 11
They are both Goofus Monday, November 7, 11
Why not cover the whole app in tests? Monday, November
7, 11
“It’s a small world, but I wouldn’t want to paint
it” Monday, November 7, 11
It’s not a quick win Monday, November 7, 11
You can introduce bugs Monday, November 7, 11
Why not just drop something in? Monday, November 7, 11
It sets a bad precedent Monday, November 7, 11
It doesn’t make anything better Monday, November 7, 11
What’s a Gallant Software Craftsman to do? Monday, November 7,
11
The basic TDD process... Monday, November 7, 11
...applied to new changes only Monday, November 7, 11
Red. Green. Refactor. Monday, November 7, 11
Over time, coverage and quality grow organically Monday, November 7,
11
Okay, it’s not that easy Monday, November 7, 11
Why not? Monday, November 7, 11
You don’t know what to test Monday, November 7, 11
It’s hard to isolate objects under test Monday, November 7,
11
A friendly reminder: git is your friend Monday, November 7,
11
Cucumber Photo by karenandbradmerson http://www.flickr.com/photos/karenandbrademerson/492770419 Monday, November 7, 11
Cucumber is independent of the code Monday, November 7, 11
Cucumber can cover a lot of the app quickly Monday,
November 7, 11
But... Monday, November 7, 11
Cucumber is slow Photo by matley0 http://www.flickr.com/photos/matley0/2973398121/ Monday, November 7,
11
And it’s not great at isolating where a problem is
Monday, November 7, 11
Test-Driven Exploration Monday, November 7, 11
It’s like TDD... with cheating Monday, November 7, 11
Red. Make it green. Refactor. Monday, November 7, 11
The code is source of truth Monday, November 7, 11
Mock Testing Monday, November 7, 11
Mocks are fast and allow unit testing Monday, November 7,
11
But they can be hard to set up Monday, November
7, 11
Isolation Monday, November 7, 11
Only touch existing methods to call your new methods Monday,
November 7, 11
def crazy_insane_method return clean_new_method if new_condition # all the old
ugly stuff end Monday, November 7, 11
Seams Photo by boogah http://www.flickr.com/photos/boogah/4541496/ Monday, November 7, 11
Default method arguments Monday, November 7, 11
def crazy_insane_method(arg, arg, new_arg = nil) # crazy insane stuff
# now with new stuff end Monday, November 7, 11
Changing behavior without touching code Monday, November 7, 11
Monday, November 7, 11
class TestPurchase < Purchase def bang # no-op end end
user.purchase << TestPurchase.new Monday, November 7, 11
class Purchase def bang # no-op end end Monday, November
7, 11
Singleton classes Monday, November 7, 11
x = Purchase.new x.def bang # no-op end Monday, November
7, 11
Duck Typing Photo by Andyofne http://www.flickr.com/photos/andyofne/3757051334/ Monday, November 7, 11
class TestPurchase def bang # no-op end end user.purchase <<
TestPurchase.new Monday, November 7, 11
Use a pebble Photo by Slideshow Bruce http://www.flickr.com/photos/springfieldhomer/39079430/ Monday, November
7, 11
class Pebble def initialize(name) @name = name end def method_missing(method_name,
*args) p "#{method_name}(#{args.join(", ")}) from #{caller_method}" self end end Monday, November 7, 11
def caller_method(depth = 1) parse_caller(caller(depth+1).first).last end def parse_caller(at) if /^(.+?):(\d+)(?::in
`(.*)')?/ =~ at file = Regexp.last_match[1] line = Regexp.last_match[2].to_i method = Regexp.last_match[3] [file, line, method] end Monday, November 7, 11
What about bad tests? Monday, November 7, 11
Make sure the suite runs Monday, November 7, 11
Tests are also code Monday, November 7, 11
The 5-minute rule Monday, November 7, 11
When to refactor Monday, November 7, 11
Simple refactors can be done at any time... Monday, November
7, 11
...as long as the tests are green Monday, November 7,
11
Especially if you can’t test without refactoring Monday, November 7,
11
More complex refactors should be tied to actual new requests
Monday, November 7, 11
And in conclusion... Monday, November 7, 11
Respect working code Monday, November 7, 11
Test at as high a level as you can Monday,
November 7, 11
Leave things better than you found them Monday, November 7,
11
Isolate code under test Monday, November 7, 11
Consider the cost of change against the cost of no
change Monday, November 7, 11
railsrx.com @noelrap Rails Test Prescriptions Rate: http://bit.ly/nrmwtest Monday, November 7,
11