Automated CSS Testing - jsday Verona

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Automated CSS Testing Not Just a Myth @jakobmattsson www.jakobm.com

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Wikipedia on ”Melodic death metal” ! Melodic death metal is an extreme subgenre of heavy metal music.   The Swedish death metal scene did much to popularize the style, which soon centered in the "Gothenburg metal" scene in Gothenburg, Sweden.

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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

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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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Mixins Variables Reuse Nesting etc. Operations

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Write Read

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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 software 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 ??? Visual Declarative Dilemma

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Let’s try!

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

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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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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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Screenshots Compare visuals before and after 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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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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Scenario: Filter the list of audio books Given some audiobooks in the collection When I visit the list of audiobooks And I search for "cor" Then I only see matching titles When I remove the filter Then I see all audiobooks again

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

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

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

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We are already running user stories No need for manual recording

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WHAT is the CORRECT LOOK?

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Red 1.Create the design you want

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Click

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Red Green 1.Create the design you want 2.Ensure consistency and compatibility

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MARK DIFFS as intended or not intended - THE SYSTEM REMEMBERS

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

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Design is manual Definition of ”correct” is manual Testing of changes is automatic!

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Design first

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No record step + No convoluted ”design spec” + This is make-believe - + Jacking into acceptance tests

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