Migrate visual testing project to percy cli

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To migrate your visual testing project to Percy CLI and unlock a more streamlined, robust workflow, here are the detailed steps: First, you’ll need to install the Percy CLI tool globally or as a dev dependency in your project. This is typically done via npm or Yarn.

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Next, identify the visual snapshots in your existing project.

If you’re using a framework like Cypress, Playwright, or Puppeteer, you’ll be looking for cy.percySnapshot, await percySnapshotpage, or similar commands.

Replace these framework-specific snapshot calls with direct calls to percy exec or percy snapshot. You’ll want to wrap your test runner commands with percy exec to ensure the Percy environment is properly initialized.

For instance, npx percy exec -- cypress run is a common pattern.

Ensure your Percy token is configured, either as an environment variable PERCY_TOKEN or via the Percy configuration file .percy.yml. Finally, run your tests through the Percy CLI.

This will automatically upload the visual snapshots to Percy for comparison, giving you immediate feedback on visual regressions.

Table of Contents

Understanding the “Why”: The Imperative for Percy CLI Migration

Migrating to Percy CLI isn’t just about swapping out a few lines of code. it’s about fundamentally leveling up your visual testing game. Think of it like upgrading from a manual, bespoke coffee grinder to a high-precision, automated burr grinder. You get consistency, speed, and better results. The “why” here boils down to efficiency, flexibility, and future-proofing your visual regression strategy. When you’re dealing with anything from large-scale web applications to complex design systems, visual consistency is paramount. A study by Capgemini found that 88% of consumers are less likely to return to a website after a bad experience, and visual glitches are a significant contributor to that. Percy CLI helps you catch these subtle, yet critical, visual deviations before they ever reach your users, safeguarding your brand and user experience.

Why Direct CLI Integration Boosts Efficiency

Integrating Percy directly via the CLI removes layers of abstraction often present in framework-specific SDKs.

This means less potential for configuration conflicts and more direct control over the snapshotting process.

For example, by using percy exec, you’re telling Percy exactly how to run your tests, ensuring the environment is perfectly set up for visual capture.

This directness reduces debugging time and increases the reliability of your visual comparisons. It’s about getting the job done with minimal fuss. Popular sap testing tools

The Flexibility Factor: Beyond Browser-Specific SDKs

While Percy’s SDKs for Cypress, Playwright, or Puppeteer are excellent starting points, they inherently tie your visual testing to that specific browser automation framework. Migrating to the CLI liberates you. You can run visual tests across different testing frameworks, integrate with custom scripts, or even snapshot static HTML files without needing a full browser automation setup. This flexibility is invaluable for diverse projects or teams using multiple testing tools. It’s about designing a system that works for your entire ecosystem, not just one part of it.

Future-Proofing Your Visual Testing Strategy

Technology evolves rapidly.

New browser versions, framework updates, and testing methodologies emerge constantly.

By relying on the Percy CLI, you’re building on a more stable and framework-agnostic foundation.

Percy Labs regularly updates the CLI to support new browser versions and features, ensuring your visual tests remain relevant and effective regardless of how your underlying testing infrastructure changes. Shift left vs shift right

This forward-thinking approach means fewer refactoring headaches down the line and more time focused on delivering value.

Pre-Migration Checklist: Setting the Stage for Success

Before you dive headfirst into migrating your visual testing project, it’s crucial to lay the groundwork. Think of this as preparing your canvas before painting a masterpiece. A little foresight here can save you hours of troubleshooting later. In the world of software development, where projects often exceed their initial budget by 27% due to poor planning as per a PwC study, a solid pre-migration checklist is your shield against avoidable delays. This stage involves verifying your Percy account, understanding your existing project setup, and ensuring all prerequisites are met.

Verifying Your Percy Account and Project Setup

First things first, ensure you have an active Percy account and that the project you intend to migrate is properly configured within Percy.

  • Access Credentials: Confirm you have your Percy token PERCY_TOKEN. This is critical for authentication. It’s best practice to store this as an environment variable in your CI/CD pipeline rather than hardcoding it.
  • Project Existence: Log into your Percy dashboard and ensure the target project exists. If it doesn’t, create it. Note the project slug, as you might need it for more complex configurations.
  • Permissions: Verify that the account or CI/CD user running the tests has the necessary permissions to upload snapshots to the specified Percy project.

Assessing Your Current Visual Testing Implementation

Take a into your existing visual testing code.

  • Framework Identification: What browser automation framework are you currently using e.g., Cypress, Playwright, Puppeteer, Selenium?
  • Snapshot Commands: Pinpoint every instance where percySnapshot or similar calls are made. Document the arguments being passed e.g., name, widths, minHeight, percyCSS. This information will be vital when translating to CLI commands or configuration.
  • Test Runner Integration: How are your tests currently being executed? Are they part of a larger script, or do you run them directly from the test runner? Understanding this helps you determine where percy exec will fit.

Necessary Installations and Updates

Ensure your local development environment and CI/CD pipelines are ready. Page object model using selenium javascript

  • Node.js: Percy CLI requires Node.js. Confirm you have a supported version installed generally, the latest LTS version is recommended. As of recent data, Node.js is used by over 50% of professional developers for web development, highlighting its widespread adoption.

  • npm/Yarn: Ensure your package manager is up-to-date.

  • Percy CLI: Install the Percy CLI globally or as a dev dependency: 

    npm install --save-dev @percy/cli
# or
npm install -g @percy/cli

    Verify the installation by running percy --version.

Step-by-Step Migration: From SDK to CLI Execution

This is where the rubber meets the road. Scroll to element in xcuitest

Migrating your visual testing project from SDK-specific integrations to Percy CLI requires a methodical approach.

It’s less about brute-force changes and more about a surgical strike on your existing code, ensuring a smooth transition without breaking your current workflow.

We’ll break this down into digestible steps, focusing on the core changes needed for a successful switch.

Remember, precision here means fewer headaches down the line.

A typical project might involve dozens, if not hundreds, of visual snapshots, so a systematic approach is key. Advanced bdd test automation

Installing and Configuring Percy CLI

The first tangible step is to ensure Percy CLI is available in your environment.

  • Installation: As mentioned in the pre-migration checklist, install the CLI:
    yarn add –dev @percy/cli

    Installing it as a dev dependency --save-dev is generally preferred for project-specific usage and better version control.

If you installed it globally, you can skip adding it as a dev dependency.

  • Authentication: The Percy CLI needs to authenticate with your Percy project. The recommended way is via the PERCY_TOKEN environment variable.
    • Local Development: Set export PERCY_TOKEN="your_percy_token_here" in your shell, or use a .env file if your project uses a library like dotenv.
    • CI/CD: Configure PERCY_TOKEN in your CI/CD pipeline’s environment variables. This is crucial for automated visual testing. For example, in GitHub Actions, you’d add it to secrets.

Replacing SDK Snapshot Calls with percy exec

This is the core of the migration. Instead of making calls like cy.percySnapshot, you’ll now run your entire test suite through percy exec. C sharp testing frameworks

  • Identify Test Runner Command: Determine the command you use to run your visual tests.
    • Example Cypress: npx cypress run
    • Example Playwright: npx playwright test
    • Example Puppeteer/custom script: node my-visual-test-script.js
  • Wrap with percy exec: Prefix your test runner command with percy exec --. The double dash -- tells percy exec to pass all subsequent arguments directly to your test runner.
    • Old Cypress SDK: cy.percySnapshot'My Page'.
    • New Cypress, using percy exec: Your Cypress tests will now not contain cy.percySnapshot. Instead, you will have regular Cypress cy.screenshot calls within your tests. Percy CLI, when wrapped around Cypress, intercepts these screenshots.
      • In your package.json scripts: 
        "scripts": {


 "test:visual": "percy exec -- cypress run"
}
  • Important Nuance: If you were using framework-specific Percy SDKs like @percy/cypress, those SDKs often handled the “snapshotting” part by taking screenshots and uploading them. When migrating to Percy CLI, you typically remove those SDK-specific percySnapshot calls. Instead, you rely on your test runner’s native screenshot capabilities e.g., cy.screenshot in Cypress, page.screenshot in Playwright/Puppeteer. The percy exec command then intelligently intercepts these screenshots and uploads them to Percy. This is a subtle but critical shift in workflow.
    • No longer: cy.percySnapshot'Homepage'.
    • Instead: cy.screenshot'Homepage'. if needed, otherwise Percy might automatically snapshot the full page at various points when wrapped around certain runners

Configuring Visuals with .percy.yml

For more granular control over your snapshots, you can create a .percy.yml configuration file in your project root.

This is where you define widths, discovery options, and other global settings.

  • Create .percy.yml: 
    # .percy.yml
version: 2
snapshot:
 widths:  # Define default widths for all snapshots
 minHeight: 1024    # Minimum height for captured pages
 percyCSS: "body { background-color: #fff !important. }" # Inject global CSS
discovery:
 networkIdleTimeout: 100 # Wait for network activity to settle
 allowedHostnames:  # Only snapshot content from these hosts
  • Benefits: This centralizes configuration, making it easier to manage consistent visual settings across your entire project. It’s especially powerful for standardizing breakpoint testing or ensuring specific elements are always rendered correctly. A well-configured .percy.yml can drastically reduce noise in your visual diffs.

Adapting Your Test Runner for Percy CLI Compatibility

The elegance of Percy CLI lies in its ability to wrap around almost any test runner.

However, to get the most out of it, you might need to make minor adjustments to how your test runner captures screenshots or manages its execution flow.

This isn’t about rewriting your entire test suite, but rather fine-tuning it to cooperate seamlessly with Percy’s snapshotting mechanism. Appium best practices

The goal is to ensure that when percy exec runs, it can correctly capture the visual state of your application at the desired moments.

Cypress Integration with percy exec

For Cypress users, the migration typically involves removing the @percy/cypress package and its associated cy.percySnapshot calls.

  • Remove Percy Cypress SDK:
    npm uninstall @percy/cypress
    yarn remove @percy/cypress

  • Clean Up commands.js: Remove any Cypress.Commands.add'percySnapshot', ... or require'@percy/cypress/for-each-helper' lines from your cypress/support/commands.js or cypress/support/index.js files.

  • Native Cypress Screenshots: If you previously relied on cy.percySnapshot to take screenshots, you’ll now use cy.screenshot. When percy exec runs Cypress, it automatically intercepts Cypress’s native cy.screenshot command and uploads those screenshots to Percy. You can pass an optional name to cy.screenshot which will be used as the snapshot name in Percy. How to perform ui testing using xcode 

    // cypress/e2e/my-visual-tests.cy.js


it'should display the homepage correctly',  => {
  cy.visit'/'.


 cy.screenshot'Homepage View'. // This will be captured by Percy exec
  cy.get'.product-card'.first.click.


 cy.screenshot'Product Detail Page'. // Another snapshot
}.

  • Running:
    percy exec — cypress run –headless

    Using --headless is generally recommended for CI/CD environments as it’s more efficient.

Playwright and Puppeteer Adjustments

For Playwright and Puppeteer, the process is quite similar.

You’ll move away from @percy/playwright or @percy/puppeteer and rely on the CLI’s ability to wrap your standard test execution.

  • Remove Percy SDKs: Validate text in pdf files using selenium

    Npm uninstall @percy/playwright @percy/puppeteer
    yarn remove @percy/playwright @percy/puppeteer

  • Native Screenshot Calls: Just like Cypress, use the native screenshot functions of Playwright or Puppeteer. The percy exec command will intercept these.

    • Playwright Example: 

      // tests/visual.spec.js


import { test, expect } from '@playwright/test'.



test'homepage visual check', async { page } => {


 await page.goto'http://localhost:3000'.


 // This screenshot will be picked up by Percy CLI


 await page.screenshot{ path: 'screenshots/homepage.png', fullPage: true }.
}.

    • Puppeteer Example:
      // visual-test.js
      const puppeteer = require’puppeteer’.

      async => { Honoring iconsofquality nicola lindgren

      const browser = await puppeteer.launch.
      const page = await browser.newPage.

      await browser.close.
      }.

    percy exec — npx playwright test

    or for Puppeteer

    percy exec — node visual-test.js

    Ensure your test runner is outputting screenshots to a known location, or that Percy CLI is configured to look in the right place. Honoring iconsofquality callum akehurst ryan

In many cases, Percy CLI’s intelligent wrapping handles this automatically.

Integrating with Other Custom Scripts or Frameworks

The beauty of percy exec is its versatility.

If you have a custom script that renders specific HTML or a less common test runner, percy exec can still work.

  • Static HTML/Storybook: For static HTML files or component libraries like Storybook, you might use Percy’s direct snapshotting without a full test runner.

    percy snapshot

    percy snapshot ./build/static-site

    Or, if Storybook is running

    percy snapshot http://localhost:9009

  • General Principle: The key is that percy exec wraps the command that ultimately generates the visual content you want to snapshot. As long as your command either renders something in a browser or produces images that Percy can capture, you’re good to go. This makes Percy CLI an incredibly adaptable tool, fitting into almost any existing development workflow.

Optimizing for Performance and Accuracy

Once you’ve successfully migrated to Percy CLI, the next frontier is optimization. This isn’t just about making things faster. it’s about making them more reliable and ensuring your visual tests deliver genuine value by accurately catching regressions and minimizing false positives. Just like a professional athlete fine-tunes their diet and training, you need to fine-tune your Percy setup. Data shows that development teams spend up to 40% of their time on debugging and fixing issues, and a significant portion of this can be attributed to flaky tests or unclear error reporting. Optimizing your Percy workflow can drastically reduce this overhead. Reduce cognitive overload in design

Strategic Snapshot Management

Not every single element on every page needs a snapshot.

Over-snapshotting can lead to increased build times, higher Percy usage, and more visual diffs to review.

  • Critical Paths Only: Focus on key user flows and critical components. Do you need a snapshot of every single modal variation, or just the most impactful ones? Prioritize pages and states that are central to your application’s functionality or brand identity.
  • Component-Level Snapshots: For UI libraries or design systems, leverage tools like Storybook or native component testing frameworks to take granular snapshots of individual components in isolation. This allows for faster feedback and easier pinpointing of visual regressions at the source. For instance, testing a button component in isolation across various states hover, active, disabled is more efficient than constantly re-testing it within every page it appears on.
  • Dynamic Content Handling: Identify and ignore dynamic content that frequently changes but isn’t relevant for visual regression e.g., timestamps, user profile images, ad banners. Use percyCSS or Percy’s DOM-shimming capabilities to hide or normalize these elements.

Leveraging Percy CLI Configuration .percy.yml

The .percy.yml file is your control center for fine-tuning.

  • widths: Carefully select the browser widths you test. Don’t test every single possible width. choose common breakpoints e.g., 375px for mobile, 768px for tablet, 1280px for desktop that represent significant layout changes. According to StatCounter, desktop screen resolutions around 1920×1080 and 1366×768 dominate, while mobile resolutions are highly fragmented. Selecting representative widths is key.
  • minHeight: Set a reasonable minHeight to ensure full-page screenshots capture enough content, especially for pages with scrollable content. A common value is 1024px or 2048px.
  • percyCSS: Inject custom CSS to normalize or hide elements. This is invaluable for:
    • Ignoring Flaky Elements: img { visibility: hidden. }
    • Normalizing Animations: * { animation: none !important. transition: none !important. }
    • Applying Theming: Ensure a consistent background for clearer diffs.
  • discovery Options:
    • networkIdleTimeout: Adjust this if your application has long-running network requests that might delay snapshot capture. Increase it if Percy is snapshotting before all content loads, decrease it for faster builds if your app loads quickly.
    • allowedHostnames: Restrict the hostnames Percy is allowed to discover, preventing it from accidentally snapshotting third-party content.

Integrating with CI/CD for Maximum Impact

Automating your Percy CLI execution within your CI/CD pipeline is non-negotiable for true efficiency.

  • Dedicated CI Job: Create a specific job or stage in your CI/CD pipeline solely for visual regression testing with Percy. This ensures that visual checks run consistently with every code change.
  • Percy Token Management: Always store your PERCY_TOKEN as a secure environment variable in your CI/CD system e.g., GitHub Actions Secrets, GitLab CI/CD Variables, Jenkins Credentials. Never hardcode it in your package.json or other source files.
  • Branching Strategy: Configure Percy to run on pull requests and feature branches. This allows developers to catch visual regressions before merging to main, preventing issues from propagating. Percy automatically creates comparisons against the base branch of the pull request, making reviews straightforward.
  • Status Checks: Enable Percy status checks in your Git provider GitHub, GitLab, Bitbucket. This provides immediate feedback in your PR UI, showing whether the Percy build passed, failed, or requires review. This integrates visual testing directly into the development workflow, making it impossible to ignore.
  • Performance Monitoring: Regularly review your Percy build times in the Percy dashboard. If builds are consistently slow, re-evaluate your snapshot strategy and percyCSS rules. A fast feedback loop ideally under 5-10 minutes for visual tests is critical for developer productivity.

By strategically managing your snapshots, leveraging .percy.yml to its fullest, and integrating seamlessly with your CI/CD, you transform visual testing from a burdensome task into a powerful, automated quality gate. How to perform sap testing

Troubleshooting Common Migration Issues

Even with the best intentions and a clear plan, migrations can sometimes throw curveballs.

When moving a visual testing project to Percy CLI, you might encounter specific issues.

This section is dedicated to helping you diagnose and resolve the most common hiccups, ensuring your migration is as smooth as possible.

Remember, debugging is a part of the process, and understanding the common failure modes can significantly reduce your frustration.

“Percy Build Failed: Could not find any snapshots”

This is a common issue when percy exec runs but doesn’t detect any screenshots to upload. Automation of regression test cases can be cost effective

  • Cause 1: Incorrect percy exec usage: You might be running percy exec without it wrapping the correct command that generates screenshots.
    • Solution: Double-check that your percy exec -- <your_test_runner_command> is syntactically correct and that <your_test_runner_command> actually runs your tests.
  • Cause 2: Missing native screenshot calls: If you previously relied on framework-specific Percy SDKs e.g., @percy/cypress which automatically took screenshots with cy.percySnapshot, you might have removed those calls but not replaced them with native screenshot commands.
    • Solution: Ensure your test suite is making explicit screenshot calls using the test runner’s native functions e.g., cy.screenshot, page.screenshot. Percy CLI often intercepts these automatically when run via percy exec.
  • Cause 3: Percy CLI not detecting your framework: In some cases, Percy CLI might not automatically detect your test runner’s screenshots.
    • Solution: Consult the Percy documentation for specific integration details for your test runner. You might need to configure @percy/cli with a specific snapshot path or ensure the test runner is run in a way that allows Percy to hook into it.

“Authentication Failed: Invalid Percy Token”

This indicates an issue with your PERCY_TOKEN.

  • Cause 1: Missing or incorrect PERCY_TOKEN environment variable: The token is not set, is misspelled, or is for the wrong project.
    • Solution: Verify your PERCY_TOKEN. Ensure it’s correctly set as an environment variable in your local shell export PERCY_TOKEN="your_token" or in your CI/CD pipeline’s secret management. Remember that tokens are case-sensitive.
  • Cause 2: Token permissions: The token might not have the necessary permissions to upload snapshots to the specified Percy project.
    • Solution: Check your Percy project settings and ensure the token has upload permissions. If you’re using a read-only token by mistake, it will fail.

Visual Diffs Showing Unexpected Changes False Positives

This happens when Percy detects visual differences that aren’t actual regressions, often due to dynamic content or rendering inconsistencies.

  • Cause 1: Dynamic Content: Timestamps, ad banners, personalized user data, or randomized elements appearing differently between runs.
    • Solution: Use percyCSS in your .percy.yml to hide these elements: 
      # .percy.yml
version: 2
snapshot:
 percyCSS: |
    .dynamic-timestamp, .ad-banner {
      visibility: hidden !important.
    • Alternatively, Percy’s DOM-shimming capabilities can help replace dynamic content with static placeholders during snapshotting.
  • Cause 2: Font Loading Issues: Fonts loading asynchronously or not consistently between environments local vs. CI.
    • Solution: Ensure fonts are properly loaded before snapshotting. You might need to add a cy.wait or page.waitForSelector for a critical element that indicates font loading completion.
  • Cause 3: CSS Animations/Transitions: Elements animating during snapshot capture.
    • Solution: Disable animations and transitions with percyCSS: 
      * {
  animation: none !important.
  transition: none !important.
}
  • Cause 4: Network Flakiness: External resources failing to load or loading slowly.
    • Solution: Increase networkIdleTimeout in .percy.yml to give your application more time to settle.
      discovery:
      networkIdleTimeout: 1000 # Wait for 1 second of network inactivity
    • Consider mocking external API calls in your tests to ensure consistent data.

Slow Build Times

Excessive build times can hinder developer productivity.

  • Cause 1: Too Many Snapshots: Taking snapshots of every single state or page, even minor ones.
    • Solution: Be selective. Focus on critical components and key user flows. Review your tests and remove redundant snapshots.
  • Cause 2: Too Many Widths: Snapshotting at an excessive number of browser widths.
    • Solution: Reduce the widths array in your .percy.yml to only essential breakpoints. Common choices are 375px, 768px, and 1280px.
  • Cause 3: Large minHeight: Setting an unnecessarily large minHeight can make snapshots take longer.
    • Solution: Set minHeight to a reasonable value e.g., 1024px or 2048px that captures the visible content without excessive blank space.
  • Cause 4: Slow Test Runner Execution: Percy can only be as fast as the tests it wraps.
    • Solution: Optimize your underlying test suite. Ensure tests are efficient, avoid unnecessary waits, and leverage parallelization if your test runner supports it.

By systematically addressing these common issues, you can streamline your Percy CLI migration and ensure your visual testing workflow is both efficient and reliable.

Best Practices for Ongoing Visual Testing

Migrating to Percy CLI is a significant step, but the journey doesn’t end there. To truly maximize the return on your investment in visual testing, you need to establish best practices for its ongoing use. Think of it as maintaining a finely tuned machine: regular checks, proper care, and continuous optimization ensure it performs at its peak. Without these practices, your visual tests can become a source of noise rather than clarity, eroding trust and slowing down development. Effective visual testing can reduce bug fixing time by 15-20% according to some agile metrics, but only if maintained properly. Top web design tools

Establish a Clear Review Process

The human element in visual testing, the review, is critical.

  • Dedicated Reviewers: Assign specific team members e.g., QA, UI/UX designers, front-end leads who are responsible for reviewing Percy builds. This ensures consistency and accountability.
  • Regular Review Cadence: Don’t let Percy builds pile up. Integrate visual reviews into your daily or weekly development rhythm. For pull requests, make it a mandatory step before merging.
  • Education and Training: Ensure all reviewers understand what constitutes a visual regression, how to approve/reject changes in Percy, and when to mark changes as “Unreviewed.”
  • Communication Channels: Use Slack, Microsoft Teams, or similar tools to notify reviewers of new Percy builds or critical visual changes. Many CI/CD tools can integrate with these platforms.

Integrate into CI/CD for Automated Feedback

Automation is the bedrock of efficient visual testing.

  • Mandatory Checks: Configure your CI/CD pipeline to make Percy a required status check for pull requests. This prevents regressions from being merged into your main branch unnoticed.
  • Branching Strategy Alignment: Ensure Percy builds are triggered for every pull request against your main development branch. Percy’s intelligent diffing automatically compares the feature branch against the base branch, providing contextual feedback.
  • Environment Consistency: Strive for consistent environments between your local development, CI/CD, and Percy’s rendering infrastructure. Differences in fonts, browser versions, or system configurations can lead to false positives. Use Docker or standardized build environments where possible.
  • “Fail Fast” Principle: Configure your CI/CD to fail the build immediately if Percy detects unapproved visual changes. This provides immediate feedback to the developer.

Maintain Your Visual Test Suite

Just like unit tests, visual tests require maintenance.

  • Regular Cleanup: Remove outdated or irrelevant snapshots. If a feature or component is removed, delete its corresponding visual tests.
  • Update Baselines: When intentional UI changes occur e.g., a redesign, new feature implementation, approve the new Percy baselines. This updates the “source of truth” for future comparisons.
  • Address Flakiness: Actively investigate and resolve any flaky visual tests those that randomly pass/fail without actual code changes. Flakiness erodes trust in the test suite. Refer back to the troubleshooting section for common causes dynamic content, animation, etc..
  • Review percyCSS and minHeight: Periodically review your .percy.yml to ensure percyCSS rules are still relevant and minHeight is appropriate for your content.
  • Performance Monitoring: Keep an eye on Percy build times. If they become consistently slow, optimize your snapshot strategy fewer widths, more targeted snapshots. A build that takes more than 10-15 minutes starts to impede developer flow.

Educate Your Team

Visual testing is a team sport.

  • Onboarding: New team members should be trained on how Percy works, how to run visual tests, and how to review Percy builds.
  • Shared Responsibility: Foster a culture where everyone developers, QA, designers understands the importance of visual quality and feels empowered to contribute to its maintenance.
  • Documentation: Maintain clear, concise documentation on your team’s visual testing process, including how to set up Percy locally, how to interpret diffs, and the review workflow.

By embedding these best practices into your development lifecycle, you transform Percy from a mere tool into a powerful, collaborative quality gate that helps maintain a pixel-perfect user experience, reflecting the care and precision encouraged in all endeavors.

Beyond the Basics: Advanced Percy CLI Usage

Once you’ve mastered the fundamentals of migrating to and using Percy CLI, you’ll discover a deeper layer of capabilities that can further refine your visual testing strategy. This isn’t just about making things work. it’s about making them work smarter, enabling more sophisticated test scenarios and tighter integration with complex project setups. Think of these as the power-user features that can handle the edge cases and optimize your workflow for truly large-scale or unique applications. Leveraging these advanced features can reduce the average time to detect and resolve defects by up to 30% by providing more precise and targeted feedback.

Snapshotting Specific Elements Component Snapshots

While full-page snapshots are valuable, sometimes you only care about the visual integrity of a specific component or section of a page.

  • Element-specific Snapshots: Percy CLI, when integrated with certain test runners, allows you to target specific DOM elements for snapshotting. Instead of capturing the entire viewport, you can tell Percy to only capture a particular component.

    • Cypress with @percy/cypress – for advanced use cases where you might re-introduce it alongside CLI: While the general recommendation is to remove SDKs, for highly specific component isolation in Cypress, some teams might re-introduce @percy/cypress alongside percy exec and use cy.percySnapshot'My Button', { element: '#my-button-id' }. This is an advanced pattern and requires careful management to avoid conflicts.

    • Playwright/Puppeteer custom scripts: You can programmatically take screenshots of elements and then upload them.
      // Example for Playwright/Puppeteer
      const elementHandle = await page.$’#my-component’.

      Await elementHandle.screenshot{ path: ‘screenshots/my-component.png’ }.

      // Then ensure Percy CLI is configured to pick up these ‘screenshots’ folder.

      // OR you can use ‘percy snapshot’ directly if generating static assets.

  • Benefits: Faster rendering, reduced noise in diffs, and highly targeted visual feedback, especially useful for design systems and component libraries where individual components are developed in isolation.

Handling Dynamic Content with Advanced percyCSS and JavaScript

Beyond simple visibility: hidden., percyCSS can be used for more nuanced control.

  • Replacing Content: You can inject CSS to replace dynamic text with static placeholders: 
    .user-name::before {
  content: "John Doe".
  display: inline-block.
 visibility: visible. /* Make sure it's visible if parent is hidden */
}
.user-name {
 visibility: hidden. /* Hide the original dynamic content */
  • Disabling Interactive Elements:
    button, a {
    pointer-events: none !important.
    cursor: default !important.
  • Client-Side JavaScript Hooks Advanced: For extremely complex dynamic scenarios, you might need to run custom JavaScript on the page before a snapshot is taken. This is often done by directly interacting with the browser instance within your test runner and manipulating the DOM or waiting for specific conditions. Percy’s underlying browser discovery mechanism can be configured to execute scripts post-load if needed, though this typically involves deeper integration specific to how Percy launches the browser.

Cross-Browser and Cross-Environment Testing

Percy’s strength lies in its ability to render across multiple browsers and environments.

  • Browser Diversity: Percy renders your snapshots in different browsers e.g., Chrome, Firefox, Safari by default, depending on your plan. This helps catch browser-specific rendering issues. Ensure your Percy project is configured to use the desired browsers.
  • Storybook Integration: If you use Storybook for component development, Percy has excellent integration. You can use percy snapshot <storybook-url> to automate visual regression for your entire component library, ensuring consistency across your design system. This is an incredibly powerful way to scale visual testing for UI components.
  • Different Deployments: You can run Percy CLI against different environments staging, production preview to compare a feature branch against a deployed baseline, providing crucial validation before production releases. This adds a layer of confidence beyond comparing against your main branch.

Customizing Percy CLI Behavior

The percy command itself offers a variety of options for specific needs.

  • percy exec --dry-run: Test your Percy integration without actually uploading snapshots to Percy. Useful for debugging your setup locally.
  • percy exec --verbose: Get detailed output during the build process, which can be invaluable for troubleshooting.
  • percy exec --skip-discovery: If you’re manually providing snapshots e.g., from pre-generated images, you might want to skip Percy’s automatic discovery phase.
  • --debug Flag: For deep troubleshooting, the --debug flag can provide extremely verbose output, including details on asset discovery and rendering processes.

These advanced techniques empower you to tackle more complex visual testing challenges, refine your feedback loop, and ensure an even higher degree of visual quality in your applications.

Remember to always prioritize simplicity and maintainability.

Use advanced features only when the problem truly warrants it.

The Islamic Perspective on Quality and Precision in Work

In Islam, there’s a profound emphasis on ihsan, which translates to excellence, perfection, or doing things beautifully and precisely. This concept extends to every aspect of life, including one’s professional endeavors and the quality of work produced. When we talk about visual testing, ensuring pixel-perfect UIs and robust, bug-free applications, we are intrinsically aligning with the principles of ihsan.

The Prophet Muhammad peace be upon him said, “Indeed, Allah loves that when one of you does a job, he perfects it.” Reported by Al-Bayhaqi. This Hadith serves as a powerful reminder for every Muslim professional: whatever task we undertake, we should strive to perform it with the utmost care, dedication, and precision. In the context of software development, this means not just making something functional, but making it excellent—visually appealing, user-friendly, and free from defects.

Why Quality Matters in Our Profession

  • Trust and Reliability: Just as trust is paramount in all dealings, users trust our applications to work flawlessly. Visual inconsistencies or bugs can erode this trust. By employing robust testing methods like Percy CLI, we are building trustworthy products.
  • Accountability: As professionals, we are accountable for the quality of our work. Negligence in ensuring visual integrity or functional correctness goes against the spirit of ihsan. Visual testing provides a systematic way to uphold this accountability.
  • Resource Stewardship: Developing and maintaining software consumes resources—time, effort, and money. When visual bugs slip through, it leads to wasted resources in fixing them post-release. Proactive visual testing is a form of good stewardship of these resources.
  • User Experience UX: Providing a seamless and aesthetically pleasing user experience is a form of service. Visual glitches, even minor ones, can detract significantly from UX, frustrating users. Striving for visual perfection is a way of serving the needs of our users with excellence.
  • Ethical Obligation: In essence, delivering a high-quality product is an ethical obligation. It reflects integrity, diligence, and respect for the end-user. Visual testing, particularly with tools that provide such precision, becomes a means to fulfill this obligation.

Avoiding “Quick Fixes” and Embracing Thoroughness

The pursuit of excellence discourages a mindset of “just enough” or “quick fixes” that might lead to compromised quality.

While speed is often a goal in modern development, it should not come at the expense of thoroughness.

Visual testing, especially with systematic tools like Percy, encourages a comprehensive approach, where every visual change is scrutinized.

This meticulousness is a reflection of the Islamic emphasis on diligence and precision in all matters.

In summary, adopting and optimizing tools like Percy CLI for visual testing isn’t just a technical decision. it’s a practical application of the Islamic principle of ihsan. It’s about ensuring that the digital products we craft are not just functional, but also visually perfect, reflecting our commitment to excellence in every detail.

Frequently Asked Questions

What is Percy CLI used for?

Percy CLI Command Line Interface is used to run visual regression tests directly from your terminal, wrapping around your existing test runners like Cypress, Playwright, Puppeteer or custom scripts.

It captures visual snapshots of your application and uploads them to Percy.io for automated visual comparison, helping you detect unintended UI changes.

How do I install Percy CLI?

You can install Percy CLI globally or as a dev dependency in your project using npm or Yarn.

The recommended method is as a dev dependency: npm install --save-dev @percy/cli or yarn add --dev @percy/cli. For global installation, use npm install -g @percy/cli.

Do I need to remove Percy SDKs e.g., @percy/cypress when migrating to Percy CLI?

Yes, generally, you should remove framework-specific Percy SDKs like @percy/cypress or @percy/playwright from your project.

When using Percy CLI, you rely on your test runner’s native screenshot capabilities, which Percy CLI then intercepts and uploads.

How do I configure Percy CLI?

Percy CLI is primarily configured via environment variables, especially PERCY_TOKEN, and through a .percy.yml file placed in your project’s root directory.

The .percy.yml file allows you to define snapshot widths, minimum heights, injected CSS percyCSS, and discovery settings.

What is the PERCY_TOKEN and why is it important?

PERCY_TOKEN is your authentication token that grants Percy CLI permission to upload snapshots to your Percy.io project.

It’s crucial for securely authenticating your builds and should always be stored as an environment variable in your local setup and especially in your CI/CD pipeline, never hardcoded in your source code.

How do I run my tests with Percy CLI?

You run your tests by wrapping your standard test runner command with percy exec. For example, percy exec -- cypress run for Cypress, or percy exec -- npx playwright test for Playwright.

The double dash -- passes subsequent arguments to your test runner.

Can Percy CLI work with any test runner?

Yes, Percy CLI is designed to be largely test runner-agnostic.

It works by wrapping your command that launches a browser and interacts with your application.

As long as your test runner can produce visual output or screenshots, Percy CLI can often intercept and upload them.

What is percyCSS and how do I use it?

percyCSS is a powerful feature within .percy.yml that allows you to inject custom CSS into your application before Percy takes a snapshot. It’s used to hide dynamic content e.g., timestamps, ads, normalize animations, or apply specific styling to ensure consistent visual comparisons and reduce false positives.

How do I handle dynamic content that causes false positives?

To handle dynamic content, you can use percyCSS to hide or stylize elements that frequently change but aren’t critical to visual regression testing.

For example, visibility: hidden !important. for dynamic elements.

You can also use minHeight or networkIdleTimeout in .percy.yml to ensure proper page loading and stability before snapshots.

What are common widths to specify in .percy.yml?

Common widths to specify in .percy.yml for visual testing include typical mobile, tablet, and desktop breakpoints.

For example, covers common smartphone, tablet, and laptop screen sizes.

Selecting representative widths is key to efficient testing.

How can I optimize Percy build times?

To optimize Percy build times, you can: be selective about which pages/components you snapshot, reduce the number of widths in your .percy.yml file, optimize your underlying test suite for faster execution, and ensure efficient asset discovery by Percy CLI.

What does “Percy Build Failed: Could not find any snapshots” mean?

This error typically means that percy exec ran successfully but didn’t detect any visual snapshots being captured by your wrapped test runner.

Common causes include: incorrect percy exec command, missing native screenshot calls in your tests, or issues with Percy CLI’s ability to intercept your test runner’s output.

How do I debug Percy CLI issues?

You can debug Percy CLI issues by using the --verbose or --debug flags with percy exec e.g., percy exec --verbose -- cypress run to get more detailed output.

Review your PERCY_TOKEN and .percy.yml configuration for any syntax errors or incorrect values. Also, check the Percy.io dashboard for build logs.

Can I run Percy CLI in a CI/CD pipeline?

Yes, Percy CLI is designed for seamless integration with CI/CD pipelines e.g., GitHub Actions, GitLab CI/CD, Jenkins. You simply configure PERCY_TOKEN as a secure environment variable in your pipeline settings and add a step to run percy exec -- <your_test_runner_command>.

How does Percy handle different browsers for visual comparison?

Percy renders your snapshots in different browsers e.g., Chrome, Firefox, Safari on its own infrastructure, independent of your local browser.

You can configure which browsers Percy should render in your Percy.io project settings or within .percy.yml though browser options are usually project-level on the Percy dashboard.

What is the role of networkIdleTimeout in .percy.yml?

networkIdleTimeout specifies how long Percy should wait for network activity to settle before taking a snapshot.

This is crucial for applications that load content asynchronously.

Increasing this value can help ensure all content is loaded, reducing false positives, while decreasing it can speed up builds for fast-loading apps.

Can I test specific UI components in isolation with Percy CLI?

Yes, you can test specific UI components by integrating Percy CLI with tools like Storybook or by using your test runner’s native capabilities to isolate and snapshot individual components.

This allows for targeted visual feedback and faster debugging.

What are the benefits of migrating to Percy CLI?

Migrating to Percy CLI offers several benefits, including: greater flexibility as it’s less tied to specific SDKs, direct control over visual testing through command-line execution, improved efficiency in CI/CD pipelines, and future-proofing your visual testing strategy by relying on a stable, framework-agnostic tool.

How do I approve or reject visual changes after a Percy build?

After a Percy build, you review the visual differences directly in the Percy.io dashboard.

For each detected change, you can either “Approve” it if it’s an intended change and becomes the new baseline or “Reject” it if it’s an unintended regression.

Is it possible to use Percy CLI for visual testing of static HTML files?

Yes, Percy CLI can directly snapshot static HTML files or entire static sites.

You can use the percy snapshot <directory_or_url> command e.g., percy snapshot ./build/static-site to upload visual snapshots of your static content without needing a full test runner setup.

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