Test Your Legacy Code - Speaker Deck

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Test Your Legacy Code Noel Rappin @noelrap Monday, November 7, 11

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You are handed a “rescue” project Monday, November 7, 11

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Oh. My. God. The last person to work on this was an idiot Monday, November 7, 11

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Now what? Monday, November 7, 11

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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

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Get back to work. Monday, November 7, 11

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What is a legacy application? Monday, November 7, 11

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Code without tests Monday, November 7, 11

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Code based on lost requirements Monday, November 7, 11

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You don’t know what “correct” means Monday, November 7, 11

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What’s your goal? Monday, November 7, 11

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Respect working code. Do no harm. Monday, November 7, 11

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Deliver features Monday, November 7, 11

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At a sustainable pace Monday, November 7, 11

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Improve code quality Monday, November 7, 11

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The Boy Scout Rule Monday, November 7, 11

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Our rescue project needs to change Monday, November 7, 11

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Goofus and Gallant Monday, November 7, 11

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“First, let’s write tests and cover the whole app” Monday, November 7, 11

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“That change is easy, I’ll just drop that in” Monday, November 7, 11

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They are both Goofus Monday, November 7, 11

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Why not cover the whole app in tests? Monday, November 7, 11

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“It’s a small world, but I wouldn’t want to paint it” Monday, November 7, 11

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It’s not a quick win Monday, November 7, 11

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You can introduce bugs Monday, November 7, 11

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Why not just drop something in? Monday, November 7, 11

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It sets a bad precedent Monday, November 7, 11

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It doesn’t make anything better Monday, November 7, 11

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What’s a Gallant Software Craftsman to do? Monday, November 7, 11

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The basic TDD process... Monday, November 7, 11

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...applied to new changes only Monday, November 7, 11

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Red. Green. Refactor. Monday, November 7, 11

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Over time, coverage and quality grow organically Monday, November 7, 11

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Okay, it’s not that easy Monday, November 7, 11

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Why not? Monday, November 7, 11

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You don’t know what to test Monday, November 7, 11

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It’s hard to isolate objects under test Monday, November 7, 11

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A friendly reminder: git is your friend Monday, November 7, 11

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Cucumber Photo by karenandbradmerson http://www.flickr.com/photos/karenandbrademerson/492770419 Monday, November 7, 11

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Cucumber is independent of the code Monday, November 7, 11

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Cucumber can cover a lot of the app quickly Monday, November 7, 11

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But... Monday, November 7, 11

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Cucumber is slow Photo by matley0 http://www.flickr.com/photos/matley0/2973398121/ Monday, November 7, 11

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And it’s not great at isolating where a problem is Monday, November 7, 11

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Test-Driven Exploration Monday, November 7, 11

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It’s like TDD... with cheating Monday, November 7, 11

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Red. Make it green. Refactor. Monday, November 7, 11

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The code is source of truth Monday, November 7, 11

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Mock Testing Monday, November 7, 11

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Mocks are fast and allow unit testing Monday, November 7, 11

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But they can be hard to set up Monday, November 7, 11

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Isolation Monday, November 7, 11

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Only touch existing methods to call your new methods Monday, November 7, 11

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def crazy_insane_method return clean_new_method if new_condition # all the old ugly stuff end Monday, November 7, 11

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Seams Photo by boogah http://www.flickr.com/photos/boogah/4541496/ Monday, November 7, 11

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Default method arguments Monday, November 7, 11

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def crazy_insane_method(arg, arg, new_arg = nil) # crazy insane stuff # now with new stuff end Monday, November 7, 11

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Changing behavior without touching code Monday, November 7, 11

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class TestPurchase < Purchase def bang # no-op end end user.purchase << TestPurchase.new Monday, November 7, 11

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class Purchase def bang # no-op end end Monday, November 7, 11

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Singleton classes Monday, November 7, 11

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x = Purchase.new x.def bang # no-op end Monday, November 7, 11

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Duck Typing Photo by Andyofne http://www.flickr.com/photos/andyofne/3757051334/ Monday, November 7, 11

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class TestPurchase def bang # no-op end end user.purchase << TestPurchase.new Monday, November 7, 11

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Use a pebble Photo by Slideshow Bruce http://www.flickr.com/photos/springfieldhomer/39079430/ Monday, November 7, 11

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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

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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

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What about bad tests? Monday, November 7, 11

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Make sure the suite runs Monday, November 7, 11

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Tests are also code Monday, November 7, 11

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The 5-minute rule Monday, November 7, 11

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When to refactor Monday, November 7, 11

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Simple refactors can be done at any time... Monday, November 7, 11

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...as long as the tests are green Monday, November 7, 11

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Especially if you can’t test without refactoring Monday, November 7, 11

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More complex refactors should be tied to actual new requests Monday, November 7, 11

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And in conclusion... Monday, November 7, 11

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Respect working code Monday, November 7, 11

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Test at as high a level as you can Monday, November 7, 11

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Leave things better than you found them Monday, November 7, 11

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Isolate code under test Monday, November 7, 11

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Consider the cost of change against the cost of no change Monday, November 7, 11

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railsrx.com @noelrap Rails Test Prescriptions Rate: http://bit.ly/nrmwtest Monday, November 7, 11