Comprehensive WordPress theme testing: your guide to robust and valid code

Creating a WordPress theme that looks great and performs flawlessly is crucial for any developer. Regardless of your experience, implementing a robust strategy for your theme testing can make the difference between a mediocre product and a standout success.

In this guide, we look at WordPress theme testing and explore the tools, techniques, and best practices that will elevate your theme’s quality. This is the guide for ensuring your theme meets the highest standards for performance, compatibility, and user experience (UX).

Understanding WordPress theme testing

Building any product requires a testing process that’s more than a final check before launch. It’s an integral part of the development process that can help you identify and rectify issues early, saving time and resources in the long run.

WordPress theme testing lets you ensure that your theme functions correctly across various environments, browsers, and devices. It can uncover issues you will need to address before publishing:

• Compatibility issues with different WordPress versions.
• Conflicts with popular plugins.
• Performance bottlenecks.
• UX inconsistencies and accessibility concerns.
• Security vulnerabilities.

While WordPress theme testing can include bug fixes, the process generally helps you craft a product that will stand out in the marketplace.

WordPress theme standards in a nutshell

WordPress has an established set of coding standards to ensure consistency and quality across themes. These standards are not just arbitrary rules; they’re the result of refinement through years of community experience and collaboration.

The Make WordPress Themes team enforces these standards for would-be inclusions within the WordPress Theme Directory:

Themes submitted to the directory undergo a thorough review to ensure they meet the platform’s quality and security requirements.

Given that the Theme Directory is the official repository — and the first place many will go to find a new theme — it’s vital that every download runs as you expect it to, without security issues or major bugs. This high standard of quality is just one aspect that makes WordPress the platform it is.

Why you should test against the WordPress standards

Meeting WordPress standards isn’t only about approval for inclusion within the Theme Directory. The deeper goal is to create a reliable, secure product that works for the user.

There are lots of compelling reasons to test your theme against WordPress standards beyond the desire to find it a home among the competition:

• Future-proofing. WordPress constantly evolves. As such, if you adhere to current standards, you make it easier to maintain and update your theme in the future.
• Compatibility. If your theme follows WordPress standards, it is more likely to work with a wide range of plugins and WordPress core features.
• Performance. Many WordPress standards focus on performance. Following these can help ensure your theme runs with greater efficiency.
• Security. The standards include best practices for security, which helps to protect your theme and its users from potential vulnerabilities.

The net result of targeting these facets is a big one: user trust. Most users will want a quality product that is secure, stable, and bug-free.

For those familiar with WordPress, a theme that meets these standards is another boost to the platform’s stellar reputation. For users coming to WordPress for the first time, quality themes will give an air of dependability. As such, it could be the start of a lifelong association with the platform, thanks to your theme.

What standards WordPress will judge your theme against

The Make WordPress Themes team is central and crucial to maintaining the quality of themes within the platform’s ecosystem. They evaluate themes based on a comprehensive set of criteria:

• Code quality. There must be no JavaScript or PHP errors, warnings, or notices. Your theme also can’t use deprecated constants or functions. WordPress also has a separate set of coding standards with which to comply.
• Functionality. You can’t “manipulate” the editing preview screens, put typical WordPress functionality behind a paywall, or carry out redirects upon activation. There are also guidelines for displaying admin notifications and including “non-presentation” functionality.
• Accessibility. Themes must include skip links and keyboard navigation options. Links must also use underlines.
• Licensing. Of course, themes must be compatible with the GNU General Public License (GPL). However, you don’t have to use the same license as WordPress — any compatible GPL license is valid.

There are also guidelines relating to promoting and presentation. For example, the Make WordPress Themes team can decide to reject your theme based on its name. This will happen where there’s a trademark infringement or you choose an inappropriate name.

In addition, there are restrictions on credit placements — even then, you can only add it to style.css:

There’s also some author account guidance, such as how many accounts you can have and theme submission frequencies. Most of the required elements center on technical development facets.

WordPress technical standards

Of the 14 requirements for submitting a theme to WordPress, those relating to theme settings, files, and whether your theme uses Blocks make up a large chunk.

When it comes to Classic themes and Block themes, you have more guidance for the former:

• Classic themes. You have to include many functions, sometimes in specific locations within your code. The same goes when calling templates.
• Block themes. Adhering to the standards for Block themes is more straightforward, as you need to include just four files. If your Block templates are also complete, your theme will meet the technical standards for a number of requirements.

There are many requirements regarding settings. For instance, you must use specific hooks to display notices and set the notice’s permanence in accordance with the review process guidelines.

There is tight control for storing options within the database. You have to use a single array, even for multiple settings, with the right naming conventions. When it comes to the WordPress dashboard, you can use only core user interface (UI) elements, and any styling has to stay within the boundaries of your theme’s admin page.

You also have to monitor the files you include within your theme. Every theme has to include a readme.txt file, for example. Preparing your files (such as removing premium code or superfluous directories) is another requirement, as is including all of the scripts and media for your theme rather than using remote sources. This also goes for minified scripts: you must also include the full, original file.

Meeting all of the WordPress requirements for your theme can seem like a hassle, especially if you don’t plan on submitting to the official directory. Even so, these standards provide an excellent framework to help you deliver a quality product.

Why meeting the WordPress standards can help the quality of your theme

To get your theme into the official directory, you must meet the Make WordPress Theme guidelines. However, consider an agency that creates custom themes for clients. Often, these themes won’t need submission to the Theme Directory, as there will be no mass distribution. But following the guidelines and requirements can still offer benefits for all WordPress themes, including:

• Consistency. The standards provide a common framework, making it easier for teams to work on a project together.
• Efficiency. You can speed up your development time by following the established standards. This can also reduce the need for extensive customizations down the line.
• Maintainability. Standardized code is easier to maintain and update. This is another way to save time and resources in the long run.
• Client satisfaction. Themes that adhere to WordPress standards have a greater chance to provide your clients a smooth, bug-free experience.

In addition to all of this, you give your theme flexibility for the future. Consider a situation where a client rejects a theme for a project, or terminates the agreement. A theme that meets WordPress standards and requirements is one you can repurpose into a product offering without a lot of extra work.

In short, even if you don’t want to target the WordPress Theme Directory, meeting the platform’s requirements can enhance the quality and marketability of your themes. At the least, you demonstrate professionalism and attention to detail, which can be a strong selling point for potential clients.

The essential tools you need for WordPress theme testing

Like any tradesperson, WordPress developers need a robust and adaptable toolkit that covers various aspects of creating a theme and making it performant.

Consider the WordPress coding standards and the requirements from the Make WordPress Themes team as your instruction booklets. You don’t need to check each of these manually, either. Instead, the Theme Check and Theme Sniffer plugins can automate it.

They both run tests on your theme and display any areas that may not meet the current requirements. Theme Sniffer has a few more comprehensive tests, and uses custom “sniffs” for the PHP_CodeSniffer script to help detect standards violations.

You’ll also want to lean on your browser’s development tools to inspect and debug your HTML, CSS, and JavaScript. For WordPress-specific debugging, it’s nearly impossible to do without the platform’s own debug mode. The Debug Bar plugin adds a debug menu to the WordPress dashboard that pulls from this mode.

There are a few other plugins that can offer value too, when testing your theme:

• Query Monitor. This tools panel provides insights into database queries, hooks, conditionals, and much more.
• Log Deprecated Notices. If your theme uses deprecated files, functions, and function arguments, this plugin will catch them. It’s a good way to keep your theme up-to-date with the latest WordPress versions.
• Monster Widget plugin. Classic Themes use widgets, and this plugin adds a single widget to your site that contains all the available core widgets. The goal is to let you test out widget areas with efficiency.

You might not use all of these plugins and tools during your WordPress theme testing workflow. That’s the point of your toolbox: each component serves a purpose and helps you fix issues before they become problems.

WordPress theme testing: setting up your testing environment

With your toolbox ready, you can set your working area. For WordPress theme testing, this means creating a proper testing and development environment. The idea is to ensure you can repeat any tests and obtain accurate results.

You might already have much of this process ready to rock without any further setup. Certainly, regular WordPress developers will have one of the following available without effort:

• A local development environment. A WordPress setup on your local machine lets you run tests without affecting your live site. DevKinsta is one of the best options available for this.
• Multiple WordPress versions. You should carry out tests against several older WordPress versions for maximum compatibility.
• Various PHP versions. By extension, these tests should run against different versions of PHP or any other important technology your theme requires.
• Popular plugins. To ensure you test against a real-world and realistic setup, it’s a good idea to install and activate some of the most popular WordPress plugins. This can be to test for compatibility issues, or to see how your theme performs with a typical load.
• Multiple devices and browsers. Testing your theme against various devices and browsers will ensure it looks great and works consistently across platforms.

Once you have the components of your environment in place, you’ll need to configure WordPress for debugging. To do this, open your wp-config.php file using the method you prefer. Secure File Transfer Protocol (SFTP) or Secure Shell (SSH) are ideal.

Once wp-config.php is open, add the following lines:

define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );

This enables WordPress debug mode, logs errors to a file, and prevents either of those from displaying on the frontend. It’s something you can also turn off again to upload the testing site to a live server.

The Theme Unit Test Data: WordPress helper content that helps you meet its theme standards

There’s one more element for WordPress theme testing that can be crucial for rooting out edge case bugs or issues: the Theme Unit Test Data. It’s an XML file that contains a wide variety of content types and edge cases, which you upload to your site through the WordPress dashboard.

Here’s why it’s so valuable:

• It includes various content types, such as posts, pages, comments, and media. This lets you test how your theme handles different content scenarios.
• The data includes elements such as very long titles, posts without titles, and nested comments. All of these edge cases are important to test, as you want the user to be able to make any customization relevant for them.
• Various formatting options ensure your theme styles content as you’d expect. The XML file includes content and media to test this.
• You have content in different languages, too, which includes lettering that could cause formatting errors.

You can find the Theme Unit Test Data XML file in the official WordPress GitHub repository or the Make WordPress Themes Handbook. Once you download this, head to the Tools > Import screen within WordPress:

This will show a list of import options for the platform, for which you want to choose Install Now for WordPress. Alternatively, you can install the WordPress Importer plugin. The install link will change to Run Importer. Click this, toopen an uploader dialog. Then, choose your XML file and click the Upload file and import button:

The content this will import comes with other user profiles. The Import WordPress screen lets you choose whether you import them alongside the content. Alternatively, you can either create your own user or assign that content to a user that already exists on your site:

It’s recommended that you check the Download and import file attachments checkbox. This mirrors a typical WordPress experience. Once you click the Submit button, WordPress will take a few moments to import the content, users, and media. From here, you can test how your theme handles various content types and scenarios to ensure it meets the content display and formatting requirements.

The fundamentals of theme testing

Having the right workflow is key to a smooth and trouble-free experience. This is especially true with a long list of extra tools and plugins to manage. Once you have a stable testing environment, you can assess the steps required for testing.

The key to WordPress theme testing is that it’s iterative and fluid. There’s no fixed, step-by-step linear workflow. Instead, there are a number of tasks you can complete in the order you choose.

For example, your workflow will likely include at least one or all of the following steps:

• Enabling debug mode.
• Running the Theme Check or Theme Sniffer plugins.
• Testing with the Theme Unit Test Data.
• Troubleshooting using browser DevTools.

Testing your theme’s options and customizations could happen at various points. This area will be revisited throughout the process. The same is true for checking plugin compatibility. These two areas will be evaluated constantly. Other tests you carry out will often revolve around these areas.

The debugging stage will often follow your testing, although there is some crossover. Ultimately, WordPress theme testing looks at areas relating to functionality, performance, security, accessibility, and code “suitability.”

Once you have a theme that passes your tests, meets the official WordPress requirements, and offers no bugs, submitting it should be simple.

The core areas of technical WordPress theme testing

With the fundamentals in mind, you can look at the core facets of testing your theme. As with the fundamentals, these core areas are fluid and iterative. However, it’s a sound idea to begin by confirming your theme handles basic functionality.

Functionality testing

In general, functionality testing ensures all aspects of your theme work as expected. A theme that cannot support default WordPress functionality is not viable. The Theme Unit Test Data is vital for this, as you can inspect how your theme handles typical situations and edge cases.

For example, you will already have posts and pages with typical and atypical content, so creating more of them is unnecessary. Testing this content is subjective and will rely on your goals, the design brief, the client’s desires, and more.

For most use cases, it’s valuable to test the following:

• For all of the typical and most popular Blocks — Paragraph, List, Image, Heading, as examples — run through how they look on the frontend. Check alignment, spacing, and general presentation for any inconsistencies.
• Multiple options will need compatibility testing. This could be with WordPress core settings, the various available Blocks, and even third-party settings for other plugins.
• If your theme will run a blog, check that the comments section displays all of its content. It’s also vital to test nested comments here so that the design and functionality work as expected.
• At this point, look for any Blocks that will integrate with your theme and test them. For instance, the Comment Block could need further adaptation. Third-party Block collection plugins might need each tested for compatibility.

For Classic themes, you should test widget areas, shortcode functionality, navigation, and other elements distinct from Block themes. However, most themes should work with the Block Editor as standard, given that it’s the future of WordPress.

Block Editor testing

Your theme will need full compatibility with the Block and Site Editors. A great place to begin is with templates, and you can find them on the Design > Templates screen within the Site Editor:

Here, you want to confirm that your templates display and that you can edit them without errors. Users may want to customize your theme’s templates and even create their own.

The Styles interface is another key customization tool within the Site Editor, which means it’s also an important factor in determining your theme’s quality.

You might play around with the settings to see if you can accomplish typical customizations. In other cases, you might work with layout settings to make everything work well together.

Other elements of Block Themes need your consideration:

• Theme.json. Thoroughly test your theme.json file to ensure it configures global styles and settings correctly.
• Block variations. If your theme uses custom Block variations, it’s important to test these in different ways .
• Custom Block templates.: For this and any relevant template parts, double-check them as you go, so you don’t introduce further bugs or errors.

This testing is in addition to technical functionality, such as ensuring all action and filter hooks work correctly. If relevant, test your theme with WooCommerce or other e-commerce plugins. Finally, many client sites will want to integrate with social media, too. Look to test any sharing buttons or feeds to ensure they function according to your client’s requirements.

Plugin compatibility

A WordPress site will likely use multiple plugins throughout its lifespan. Because there are so many plugins and combinations, it’s hard to account for every use case.

This can be a headache. Even though it’s clear you have to test your theme with some plugins, it’s tough to know which ones. Our advice is to test using a little of everything:

• The most popular page builder plugins, such as Elementor, Beaver Builder, Bricks, Brizy, and Divi.
• Most sites will have a search engine optimization (SEO) plugin such as Yoast SEO. We also recommend taking a look at SEOPress, along with many others.
• Caching plugins are common, too. WP Super Cache, W3 Total Cache, and WP Rocket are all leaders in the field.
• You can find many different form plugins, but Ninja Forms, Contact Form 7, WPForms, and Gravity Forms all frequently appear.
• Automattic and the Make WordPress Core team’s plugins should be on your list of test solutions. Akismet, Jetpack, and even the Classic Editor plugin should all have thorough testing.

You want to look for noticeable conflicts and then work on minor issues. Many themes use plugin compatibility in their marketing materials, so dedicating time to this area can boost your credibility.

Accessibility testing

Not every user has the privilege of perfect sight or working limbs. This should not be a barrier to using your theme, which means you need to perform accessibility tests before you launch.

WordPress has its own accessibility guidelines courtesy of the Make WordPress Accessible team. A sound approach to take with your own testing is to study the most beneficial accessibility practices. There are many to consider, and they come in a number of categories:

• Development. This covers aspects such as using pagination rather than infinite scrolling, labeling web forms correctly, using semantic HTML, implementing the correct header hierarchy, and much more.
• Content. These practices are straightforward, such as opening links in the same tab, adding ALT text descriptions, and applying readability.
• Design. Font sizing and color contrast are big topics when it comes to accessibility, so you should focus on them during development. The testing stage is more for refinement.

Many of these practices will also be compatible with and aligned with the Web Content Accessibility Guidelines (WCAG) 2.0. You can find checklists to help you catch and test elements related to web accessibility. Going through the development, content, and design checks will give your theme a great foundation. There are even full courses to learn about applying web accessibility testing to your projects.

Accessibility testing tools

When it comes to suitable tools, there are two recommendations:

• axe. Deque’s axe runs as part of your browser’s DevTools and automates a series of tests (depending on your account) within seconds.
• WAVE. WebAIMs WAVE is a tool you can use either in a browser or through an extension.

Using both of these tools together is an excellent way to test accessibility. For instance, you can start with a quick run-through of an axe test:

This is as simple as clicking to start a full-page scan. The results highlight areas to consider and potential ways to fix them.

WAVE can look overwhelming, especially if you have a large number of issues to resolve. However, its summary of content order and structure is invaluable to assess how your theme will work with screen readers:

It’s a good approach to clear broad issues with axe, such as general color contrast warnings, and then get into deeper accessibility concerns using WAVE. This way, you should have content with the right heading hierarchy and structure, accessible form inputs, and labeling.

You may even want to test the keyboard navigation and use your theme with a screen reader to understand the user’s experience. Either way, testing your theme’s accessibility isn’t simply a “nice-to-have” aspect—it’s essential for creating an inclusive web.

Performance testing

Testing your theme’s performance ensures it runs well for users. It can also be a key angle in your marketing. Many themes promote stellar performance, proving how important that is.

The same methodology for testing web performance will also apply to WordPress theme testing. There’s a thorough way to achieve this, although your tools may differ.

For example, Google’s PageSpeedInsights or Lighthouse are ideal. A tool like WebPageTest may be a good alternative if you want a second opinion. Regardless, there are plenty of performance testing tools available to fit your exact needs.

When it comes to what to test, there are a few key areas to focus on:

• Your Core Web Vitals should always be healthy, as this is the foundation of your theme’s performance.
• Minimizing HTTP requests and optimizing asset loading will help you manage resources better.
• Query Monitor will help you to identify and optimize any database queries.
• If your theme includes bundled images, ensure they have the optimum sizing, and you compress them before packaging them.

Your responsive or adaptive design choice should be made early in your theme’s development. Whichever you choose, you must test it to confirm it works as you intend. You don’t want to introduce horizontal scrolling, the need for content zooming, small touch targets, or display layouts that don’t adjust to the screen size.

At this point, you can undertake cross-browser testing. BrowserStack is a great tool for the job:

Finally, while server response times don’t directly relate to theme testing, they will be important for your end users. You could recommend suitable providers within your documentation or marketing. Of course, Kinsta is blazingly fast, robust, and secure.

Security testing

WordPress security testing should be a top priority for you. The WordPress team provides plenty of documentation on making sure your theme is safe to use.

Keep these principles in mind:

• Validate and sanitize all data you accept through your theme. It’s a good idea to take a cautious approach when it comes to user input and prefer validation over sanitation.
• For untrusted sources, escape everything as late as possible — usually at the output stage.
• Lean on the WordPress APIs, as these will be safe ways to handle any data within your theme.
• WordPress nonces are hashes that help protect, validate, and authenticate requests. They aren’t a front-line method of protection but can help bolster the security you already have in place.

Cross-Site Scripting (XSS), Cross-Site Request Forgeries (CSRF), and SQL injections represent some of the most common vulnerabilities for WordPress websites. Your theme should be watertight when it comes to protecting against them. Following these core principles of theme security gets you as close as possible to that goal.

Typical practices to make your theme development workflow smoother

Developing themes within an agency setting requires a different approach than solo or small projects. You need more structure, consistency, and efficiency. This can be achieved by developing your own in-house coding standards to complement those of WordPress. Collaborative workflows using Jira or Trello could be used to track issues and bugs.

When it comes to ensuring your team aligns with the overall need for quality, there are a few practices that can help:

• Implement a peer review process. This could be as simple as having team members review each other’s code before merges. In other situations, you might also consider pair programming.
• Develop reusable components. Creating a library of reusable code snippets and components can supercharge your development time. In some cases, you may even build a complete framework for creating future themes.
• Implement comprehensive testing procedures. You might want to develop a standardized testing checklist, or include user acceptance testing (UAT) in your workflow.

Some of these implementations cover typical DevOps practices and can improve the quality of your agency’s work. For instance, Continuous Integration and Continuous Deployment (CI/CD) is one of the best implementations you can make. With the right tools in your pipeline, this can help you automate your testing process in a number of ways. CI/CD is also straightforward to slot into your existing workflow and can save precious hours of testing.

Summary

WordPress theme testing is necessary to ensure your product is robust, reliable, and works for your users. Adhering to official WordPress standards and requirements is non-negotiable if you want to publish it in the WordPress Theme Directory. These guidelines also have merit for theme development by agencies and others who are not publishing for public consumption.

Regardless, comprehensive WordPress theme testing is an investment that requires time and effort. If you cover the core areas that matter — functionality, accessibility, performance, security, and code quality — you will deliver for your clients. Meeting WordPress standards might make it easier to repurpose a theme in the future once a client relationship ends.

Do you have any advice on WordPress theme testing based on your own experience? Share in the comments section below!

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