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Jakob Mattsson @jakobmattsson Developer • Entrepreneur • Crazy person

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2 000 000 000 writes/day!

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Quick and easy customer feedback. touch-and-tell.se

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Automated CSS Testing Not Just a Myth

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The purpose of this presentation: Raise awareness of existing tools Inspire a new workflow Get your help

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The purpose of this presentation: Raise awareness of existing tools Inspire a new workflow Get your help

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The purpose of this presentation: Raise awareness of existing tools Inspire a new workflow Get your help

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The purpose of this presentation: Raise awareness of existing tools Inspire a new workflow Get your help

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Declarative programming

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Declarative programming is a programming paradigm that expresses the logic of a computation without describing its control flow.” “

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Do not try it @127.0.0.1

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Mixins Variables Reuse Nesting etc. Operations

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Write Read

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New styles are added instead of reuse

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New styles are added instead of reuse Unused styles are not removed

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New styles are added instead of reuse Unused styles are not removed No overview of how different styles interact

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New styles are added instead of reuse Unused styles are not removed No overview of how different styles interact Form factors, adaptiveness, responsiveness

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New styles are added instead of reuse Unused styles are not removed No overview of how different styles interact Form factors, adaptiveness, responsiveness The true ”write-only” language

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In computer humor, a write-only language is a programming language with syntax (or semantics) sufficiently dense and bizarre that any routine of significant size is too difficult to understand by other programmers and cannot be safely edited.” “

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Code quality

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Functional quality—fitness for purpose Structural quality—the degree to which the so!ware was produced correctly

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Structural quality Reliability Maintainability Size Efficiency Security

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HOW?

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By writing automated TESTS!

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Refactor Red Green 1.Write a test that fails 2.Make the code work 3.Eliminate redundancy

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Testing CSS

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Code ??? Profit Declarative Dilemma

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Let’s try!

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1 2 3 4 Two for code Two for result { { Four approaches

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1

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Syntax Checks Checking that the code is actually valid CSS Typically performed by an editor, IDE or plugin

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2

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Styleguides & linting Forces best-practices to be followed Syntactically (where to put braces) Semantically (catching common mistakes)

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Useless without good rules + - Prevents anti-patterns Easy to apply Doesn’t test the end result - - +

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3

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Screenshots Compare visuals before and a"er change Detects impact of change

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Lots of false positives + - No change can sneak by Implementation agnostic Breaks on content changes - - +

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4

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Comparing styles in the DOM Sniff the DOM for all relevant styles Compare them to some expectation

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Scenario: Standard paragraph color Given I visit "http://localhost:3000" Then "section > p" should have "color" of "rgb(68, 68, 68)"

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Style rules != looks + - Resilient to changes Tests live on Writing expectations in code - - +

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WHAT is the MISSING PIECE?

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Design first

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Refactor Red Green 1.Write a test that fails 2.Make the code work 3.Eliminate redundancy

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My suggestion: 1. Create the design you want 2. Ensure consistency and compatibility 3. Eliminate redundancy

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My suggestion: 1. Create the design you want 2. Ensure consistency and compatibility 3. Eliminate redundancy

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My suggestion: 1. Create the design you want 2. Ensure consistency and compatibility 3. Eliminate redundancy

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My suggestion: 1. Create the design you want 2. Ensure consistency and compatibility 3. Eliminate redundancy

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Refactor Red Green 1.Create the design you want 2.Ensure consistency and compatibility 3.Eliminate redundancy

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Click

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Examples

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ul:last-child { color: red; } Won’t work in IE8. Will be caught when test runs there. #footer { width: calc(100% - 3em); } Won’t work on Android or Safari < 6 Unsupported CSS-style used

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CSS-inconsistency across browsers h1, h2, h3, h4, h5, h6, a { display: block; } ul { list-style-position: inside; }

  • Foobar

      • Chrome Firefox

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body { margin:0; padding:0; } div { margin:0; padding:10; }
Foobar
body { margin:10; padding:0; } div { margin:0; padding:0; }
Foobar
Detecting equivalent styles This change does not trigger an error; the rendered result is the same, even though styles differ.

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Now what?

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Join in!

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Automated CSS Testing Not Just a Myth @jakobmattsson • [email protected] github.com/leanmachine/testbit

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Automated CSS Testing Not Just a Myth @jakobmattsson • [email protected] github.com/leanmachine/testbit bit.ly/jakob-mmwcon + -