Javascript

How to Run End-to-End Tests on Vercel Preview Deployments

Published Sep 20, 2024

Updated Sep 20, 2024

3 min read

How to Run End-to-End Tests on Vercel Preview Deployments

End-to-end (E2E) tests are an essential part of modern web development. They simulate real user interactions and ensure your application works as expected in a live environment. When you're working with platforms like Vercel, which provide seamless deployment experiences, running E2E tests on preview deployments makes sense to catch any issues before merging your changes into the main branch.

However, running E2E tests on preview deployments can be challenging as if the deployment isn’t ready when the tests start running, you’ll get errors when they should have succeeded.

The Challenge: Timing Your E2E Tests

Imagine you're working on a feature and pushing your changes to a branch. Vercel starts deploying the preview, and once that's done, you want to run your E2E tests automatically. But if the deployment isn't ready when the tests start, they might fail, and you'll be left wondering if the issue is with your code or the deployment process.

Github Actions allow us to leverage a combination of actions that work together to ensure that your E2E tests only start once the Vercel deployment is ready.

The Solution: Combining GitHub Actions for Seamless Testing

To solve this problem, we can use two GitHub Actions in tandem:

vercel-preview-url: This action retrieves the preview URL of the Vercel deployment. It runs on push and pull request events, ensuring you get the exact URL of your deployment, which can then be used for further tests or other integrations.
github-action-await-vercel: This action waits until the Vercel deployment is marked as "READY". It continuously checks the deployment status, ensuring your tests only run once the deployment is fully prepared.

jobs:
  e2e-tests:
    runs-on: ubuntu-latest
    steps:
      # Step 1: Retrieve the Vercel Preview URL
      - name: vercel-preview-url
        uses: zentered/vercel-preview-url@v1.1.9
        if: github.event_name != 'pull_request'
        id: vercel_preview_url
        env:
          VERCEL_TOKEN: ${{ secrets.VERCEL_TOKEN }}
          GITHUB_REF: "main"
          GITHUB_REPOSITORY: "your-repo/your-project"
        with:
          vercel_project_id: ${{ secrets.VERCEL_PROJECT_ID }}

      # Step 2: Wait for the Vercel deployment to be ready
      - uses: UnlyEd/github-action-await-vercel@v1
        id: await-vercel
        if: github.event_name != 'pull_request'
        env:
          VERCEL_TOKEN: ${{ secrets.VERCEL_TOKEN }}
        with:
          deployment-url: ${{ steps.vercel_preview_url.outputs.preview_url }}
          timeout: 420
          poll-interval: 15

      # Step 3: Run your end-to-end tests
      - name: Run E2E Tests
        run: npm run test:e2e

Breaking Down the Workflow

Fetch the Preview URL: The vercel-preview-url action first retrieves the URL of the Vercel deployment. This URL is unique to the deployment, and we need to know it to run our E2E tests against the correct environment. This step ensures that we have the right URL before proceeding to the next steps.
Await Deployment Readiness: The github-action-await-vercel action waits for the deployment to be fully ready. It checks the deployment status at intervals (e.g., every 15 seconds) and only proceeds once the deployment is marked as "READY." This step ensures that your E2E tests don't run prematurely, preventing false failures.
Run E2E Tests: Once the deployment is ready, your E2E tests are executed against the live preview. By this point, you can be confident that the environment is fully set up, and any failures will likely be due to actual issues in the code rather than deployment timing.

Why This Workflow Matters

This workflow is essential for teams that rely on automated testing as part of their CI/CD pipelines. By waiting for the Vercel deployment to be fully ready, you minimize the risk of flaky tests that fail due to timing issues rather than code problems. This approach saves time and effort, as developers can focus on fixing real bugs rather than troubleshooting deployment issues.

Moreover, this setup is flexible and can be adapted to various project needs. Whether you're running tests on a simple static site or a complex application, ensuring that your deployment is ready before running tests can dramatically improve the reliability of your CI/CD pipeline.

Conclusion

In modern web development, ensuring the reliability of your CI/CD pipeline is crucial. By leveraging GitHub Actions like vercel-preview-url and github-action-await-vercel, you can confidently run E2E tests on Vercel preview deployments.

However, remember that the Vercel deployment can take some time to deploy, especially for larger projects, so use this approach wisely and ensure you only run it when necessary.

This Dot is a consultancy dedicated to guiding companies through their modernization and digital transformation journeys. Specializing in replatforming, modernizing, and launching new initiatives, we stand out by taking true ownership of your engineering projects.

We love helping teams with projects that have missed their deadlines or helping keep your strategic digital initiatives on course. Check out our case studies and our clients that trust us with their engineering.

Jan Kaiser

Software engineer passionate about everything web-related. Particularly loves Angular, SCSS, TypeScript, soccer and dachshunds

@honzikec @honzikec

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Introduction In my last post, Quick Guide to Playwright Fixtures: Enhancing Your Tests, I delved into some of the enhancements we've been implementing in our end-to-end (E2E) tests using Playwright. As I refine our testing strategies, I've come across a tool that has quickly become an essential part of my workflow: the Playwright VSCode extension. If you're like me and constantly looking for ways to streamline testing and debugging, you'll appreciate any tool that can make the process more efficient and enjoyable. That's where this extension comes in. It's not just about writing tests - it's about enhancing the entire development experience. In this post, I'll walk you through getting started with the Playwright VSCode extension, sharing some tips and tricks that have made a real difference in my day-to-day work. Installing the Extension & Basic Setup Before diving into the Playwright VSCode extension, it's essential to have Playwright installed on your machine. 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5 mins

VSCodeTestingPlaywright

Why is My React Reducer Called Twice and What the Heck is a Pure Function?

Why is My React Reducer Called Twice and What the Heck is a Pure Function? In a recent project, we encountered an interesting issue: our React reducer was dispatching twice, producing incorrect values, such as incrementing a number in increments of two. We hopped on a pairing session and started debugging. Eventually, we got to the root of the problem and learned the importance of pure functions in functional programming. This article will explain why our reducer was being dispatched twice, what pure functions are, and how React's strict mode helped us identify a bug in our code. The Issue We noticed that our useReducer hook was causing the reducer function to be called twice for every action dispatched. Initially, we were confused about this behavior and thought it might be a bug in React. Additionally, we had one of the dispatches inside a useEffect, which caused it to be called twice due to React strict mode, effectively firing the reducer four times and further complicating our debugging process. However, we knew that React's strict mode caused useEffect to be called twice, so it didn't take very long to realize that the issue was not with React but with how we had implemented our reducer function. React Strict Mode React's strict mode is a tool for highlighting potential problems in an application. It intentionally double-invokes specific lifecycle methods and hooks (like useReducer and useEffect) to help developers identify side effects. This behavior exposed our issue, as we had reducers that were not pure functions. What is a Pure Function? A pure function is a function that: - Is deterministic: Given the same input, always returns the same output. - Does Not Have Side Effects: Does not alter any external state or have observable interactions with the outside world. In the context of a reducer, this means the function should not: - Modify its arguments - Perform any I/O operations (like network requests or logging) - Generate random numbers - Depend on any external state Pure functions are predictable and testable. They help prevent bugs and make code easier to reason about. In the context of React, pure functions are essential for reducers because they ensure that the state transitions are predictable and consistent. The Root Cause: Impure Reducers Our reducers were not pure functions. They were altering external state and had side effects, which caused inconsistent behavior when React's strict mode double-invoked them. This led to unexpected results and made debugging more difficult. The Solution: Make Reducers Pure To resolve this issue, we refactored our reducers to ensure they were pure functions. Here's an extended example of how we transformed an impure reducer into a pure one in a more complex scenario involving a task management application. Let's start with the initial state and action types: ` And here's the impure reducer similar to what we had initially: ` This reducer is impure because it directly modifies the state object, which is a side effect. To make it pure, we must create a new state object for every action and return it without modifying the original state. Here's the refactored pure reducer: ` Key Changes: - Direct State Modification: In the impure reducer, the state is directly modified (e.g., state.tasks.push(action.payload)). This causes side effects and violates the principles of pure functions. - Side Effects: The impure reducer included side effects such as logging and direct state changes. The pure reducer eliminates these side effects, ensuring consistent and predictable behavior. I've created an interactive example to demonstrate the difference between impure and pure reducers in a React application. Despite the RESET_TASKS action being implemented similarly in both reducers, you'll notice that the impure reducer does not reset the tasks correctly. This problem happens because the impure reducer directly modifies the state, leading to unexpected behavior. Check out the embedded StackBlitz example below: Conclusion Our experience with the reducer dispatching twice was a valuable lesson in the importance of pure functions in React. Thanks to React's strict mode, we identified and fixed impure reducers, leading to more predictable and maintainable code. If you encounter similar issues, ensure your reducers are pure functions and leverage React strict mode to catch potential problems early in development. By embracing functional programming principles, you can write cleaner, more reliable code that is easier to debug and maintain....

Jun 14, 2024

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How to Truncate Strings Easily with CSS

You'll often need to truncate text when working with user interfaces, especially when displaying content within a limited space. CSS provides a straightforward way to handle this scenario, ensuring that long text strings are cut off gracefully without affecting the overall layout. CSS Truncation Techniques Single-Line Truncation If you want to truncate a single line of text, CSS provides a simple solution. The key properties to use here are overflow, white-space, and text-overflow. ` Explanation of properties: * white-space: nowrap: This ensures the text stays on a single line, preventing wrapping. * overflow: hidden: This hides any content that overflows the container. * text-overflow: ellipsis: This adds the ellipsis (…) at the end of the truncated text. Multi-Line Truncation While truncating a single line of text is common, sometimes you may want to display multiple lines but still cut off the text when it exceeds a certain number of lines. You can use a combination of CSS properties such as -webkit-line-clamp along with the display and overflow properties. ` Live example: Explanation of properties: * display: -webkit-box: This is a legacy flexbox-like display property that works with the -webkit-line-clamp property. * -webkit-line-clamp: Specifies the number of lines to show before truncating. * -webkit-box-orient: vertical: Ensures the box is laid out vertically for proper multi-line truncation. * overflow: hidden: Prevents content overflow. * text-overflow: ellipsis: Adds an ellipsis after the truncated content. Why Use CSS for Text Truncation Over JavaScript Techniques? While it’s possible to truncate text using JavaScript, CSS is often a better choice for this task for several reasons. Let's explore why CSS-based truncation techniques are generally preferred over JavaScript. Performance Efficiency CSS operates directly within the browser's layout engine, meaning it doesn’t require additional processing or event handling as JavaScript does. When using JavaScript to truncate text, the script needs to run on page load (or after DOM manipulation), and sometimes, it needs to listen for events such as window resizing to adjust truncation. This can introduce unnecessary overhead, especially in complex or resource-constrained environments like mobile devices. CSS, on the other hand, is declarative. Once applied, it allows the browser to handle text rendering without any further execution or processing. This leads to faster load times and a smoother user experience. Simplicity and Maintainability CSS solutions are much simpler to implement and maintain than their JavaScript counterparts. All it takes is a few lines of CSS to implement truncation. In contrast, a JavaScript solution would require you to write and maintain a function that manually trims strings, inserts ellipses, and re-adjusts the text whenever the window is resized. Here's the JavaScript Truncation Example to compare the complexity: JavaScript Truncation Example: ` At the example above, we truncated the text to 50 characters which may be 1 line on large screens and 6 lines on mobile and in that case we will need to add more code to truncate it responsively. As you can see, the CSS solution we used earlier is more concise and readable, whereas the JavaScript version is more verbose and requires managing the string length manually. Responsiveness Without Extra Code With CSS, truncation can adapt automatically to different screen sizes and layouts. You can use relative units (like percentages or vw/vh), media queries, or flexbox/grid properties to ensure the text truncates appropriately in various contexts. If you were using JavaScript, you’d need to write additional logic to detect changes in the viewport size and update the truncation manually. This would likely involve adding event listeners for window resize events, which can degrade performance and lead to more complex code. CSS Example for Responsive Truncation: ` To achieve this in JavaScript, you’d need to add more code to handle the width adjustments dynamically, making it more complex to maintain and troubleshoot. Separation of Concerns CSS handles the presentation layer of your website, while JavaScript should focus on dynamic functionality or data manipulation. By keeping truncation logic within your CSS, you're adhering to the principle of separation of concerns, where each layer of your web application has a clear, well-defined role. Using JavaScript for visual tasks like truncation mixes these concerns, making your codebase harder to maintain, debug, and scale. CSS is purpose-built for layout and visual control, and truncation is naturally a part of that domain. Browser Support and Cross-Browser Consistency Modern CSS properties like text-overflow and -webkit-line-clamp are widely supported across all major browsers. This means that CSS solutions for truncation are generally consistent and reliable. JavaScript solutions, on the other hand, may behave differently depending on the browser environment and require additional testing and handling for cross-browser compatibility. While older browsers may not support specific CSS truncation techniques (e.g., multi-line truncation), fallback options (like single-line truncation) can be easily managed through CSS alone. With JavaScript, more complex logic might be required to handle such situations. Reduced Risk of Layout Shifting JavaScript-based text truncation risks causing layout shifting, especially during initial page loads or window resizes. The browser may need to recalculate the layout multiple times, leading to content flashing or jumpy behavior as text truncation is applied. CSS-based truncation is applied as part of the browser’s natural rendering flow, eliminating this risk and ensuring a smoother experience for the user. Conclusion CSS is the optimal solution for truncating text in most cases due to its simplicity, efficiency, and responsiveness. It leverages the power of the browser’s rendering engine, avoids the overhead of JavaScript, and keeps your code clean and maintainable. While JavaScript truncation has its use cases, CSS should always be your go-to solution for truncating strings, especially in static or predictable layouts. If you like this post, check out the other CSS posts on our blog!...

Sep 13, 2024

4 mins

CSS

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How to Run End-to-End Tests on Vercel Preview Deployments

How to Run End-to-End Tests on Vercel Preview Deployments

The Challenge: Timing Your E2E Tests

The Solution: Combining GitHub Actions for Seamless Testing

Breaking Down the Workflow

Why This Workflow Matters

Conclusion

Jan Kaiser

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