Renderers are the services that take a render array and convert it to HTML (or JSON, or any other format). As a module developer, understanding how they work will help you gain a better understanding of what happens behind the scenes when Drupal links an incoming request to your custom controller and then handles the data you return.

In this tutorial we'll:

• Define renderers
• List the renderers available in Drupal core
• Demonstrate how you can create a link that forces the use of a different renderer

By the end of this tutorial, you should understand the role that renderers play in the Drupal render pipeline and when you might want to use one other than the default.

The Render API consists of two parts: structured arrays that provide data and hints about how that data should be rendered, and a rendering pipeline that can be used to render these arrays into various output formats. Understanding at least the basics of how the Render API works, the difference between elements and properties, and the concept of callback functions is an integral part of learning Drupal.

In this tutorial we'll:

• Look at the fundamentals of the Drupal Render API
• Point to additional material to provide more detail about the inner workings of the Render API and how content is output in Drupal

The core structure of Drupal's Render API is the render array, which is a hierarchical associative array containing data to be rendered and properties describing how the data should be rendered. As a module developer you'll use render arrays to describe the content your module controls in order to output it on a page as HTML, or as part of a response in another format like JSON. As a theme developer, you'll manipulate render arrays in order to affect the way content is output on the page.

In this tutorial we'll learn:

• What render arrays are and why they exist
• The basic format of a render array
• What "properties" and "elements" signify in the context of a render array
• Where to find more information about how to create a render array to describe your own content

By the end of this tutorial you should be able to understand when you need to use a render array, recognize one when you see it, and know where to get more detailed information about render array formatting specifics.

The individual items that make up the content of a page impact the cacheability of that page. In order for Drupal's cache and external caches to better understand how the content varies on a page, module developers use the #cache render element property. The #cache property defines cacheability metadata for individual elements in a render array.

Additionally, these Render API elements can become fairly complex. The calculation of what the final HTML output should look like often involves looking up content in the database, checking multiple conditions, maybe querying an external API, and various other tasks. This can cause turning a render array into HTML to become quite expensive. In order to speed up this process, the Render API will cache the generated HTML for each element and reuse it on future requests whenever possible -- but only if you tell it to do so.

In this tutorial, we'll look at:

• How render caching impacts the performance of a page
• Defining the cacheability of an item with cache tags, cache contexts, and cache max-age
• Examples of using the #cache property in a render array

By the end of this tutorial you should know how, and when, to use the #cache property when defining render arrays.

One of the central components of Drupal's Render API is render elements. You can think of them as prepackaged render arrays or shortcuts you can use to describe common things, like tables, links, and form elements, in a consistent way. In this tutorial we'll take a more in-depth look at the use of the #type property in render arrays in order to answer questions like:

• What are render elements, and what is their use case?
• Where can I find more information about available element types?

By the end of this tutorial you should be able to identify individual render element types within a larger render array, find the relevant documentation for specific types of render elements, and explain the use case for render elements.

This tutorial looks at the steps that Drupal goes through to obtain a render array for an incoming HTTP request, transform the render array into HTML, and then return it to your browser. We provide an outline of the process and links to resources for more in-depth information. We also take a more thorough look at the HtmlRenderer which converts a render array into HTML. Knowing how the render arrays you write in your code are ultimately used can help you optimize Drupal's Render API to describe your module's content.

The #table render element type is a powerful way to output an array of rows and columns as an HTML table. It supports all the features of a standard HTML <table> element like headers, captions, and column groups. Data to be displayed in the table can be an array of simple string values, or an array of render arrays where each sub element is a row with columns as child elements. In addition, when used in the context of a form, tables can be made into a multiple select widget, or have drag-and-drop reordering of rows enabled. Whether you just want to display a set of tabular data, or you provide your users with a complex form element for reordering and nesting items inside a menu tree, it can all be done with the #table element.

In this tutorial we'll:

• Look at outputting simple strings as a table
• Provide definitions for all the various properties that can be used to define a table element
• Demonstrate how to use the #tableselect and #tabledrag options to create complex form widgets

By the end of this tutorial you should be able to create HTML tables in all their various permutations as part of a render array.

In this tutorial we'll look at how you can use the #theme property of a render array to define custom HTML. With this information, module developers can use render arrays to define content, and theme developers can understand how elements in a render array are converted to HTML and which templates they can override to change the output for a specific element.

Learn how to:

• Use hook_theme() to define a new theme hook and define default values for variables
• Create a corresponding Twig template file that outputs the variables and any custom HTML markup
• Use a preprocess function to add additional variables for the Twig template file you created
• Use the new theme hook in conjunction with a #theme property in a render array to link your Twig template file to actual content

By the end of this tutorial you should know how to define new templates to output content as HTML. You should also have a better understanding of how Twig template files are linked to elements in a render array.

There are a bunch of existing render elements, most commonly Form API elements. You need to know how to discover and make use of existing elements. In this tutorial, we'll learn how to:

• Locate a list of elements provided by Drupal core
• Figure out what properties apply to each element
• Use any render element type when defining content or forms in our code

By the end of this tutorial you should know what render element types are available for you to use, and how to find the details you'll need in order to implement them in your own render arrays.

It's best practice to access any of the services provided by Drupal via the service container to ensure the decoupled nature of these systems is respected. In order to do so, you need to know what services exists, and then, where possible, use dependency injection to use them in your code.

This tutorial walks through the process of:

• Discovering existing services and learn their machine name
• Using the machine name of service to request a copy from the service container

Want to know if the person that's viewing your custom block is authenticated? Need to change the elements visible on the page based on a user's permissions or roles? Want to display a welcome message for users returning to your site?

All of these things require knowing who the user is that's currently accessing a page. This can be accomplished by using the current_user service to load an object that contains information about the current user as well as methods for checking permissions and retrieving additional information.

In this tutorial we'll:

• Define what "current user" means
• Use the current_user service to retrieve an implementation of \Drupal\Core\Session\AccountInterface
• Retrieve information about, and check the permissions of, the current user
• Add cacheability metadata when rendering user-specific output

By the end of this tutorial you should be able to retrieve and make use of information about the application's current user in order to perform logic in your code that customizes the response for different users.

In order to run tests, your Drupal site needs additional development requirements installed using Composer.

By default, when you download Drupal as a zip file or tarball, these packages will not be installed, since they're used for development purposes.

In this tutorial, we'll walk through the steps to make sure we've got Composer available. Next we'll install the dependencies. Then we'll talk about why you shouldn't have development dependencies available on your production site. Thankfully, Composer can help make this easy to manage.

Simpletest has been removed from Drupal 9. If you're preparing to upgrade your site to the latest version of Drupal and you have Simpletests in your codebase that extend WebTestBase you'll need to update them to use PHPUnit's BrowserTestBase class instead. This will ensure your tests don't depend on a deprecated testing framework. By the end of this tutorial, you should be able to convert WebTestBase-based tests to use PHPUnit's BrowserTestBase class instead.

In this tutorial, we will look at the various types of tests and testing frameworks included in Drupal core. We'll also provide an overview of how the different frameworks operate and the types of situations where each of the different frameworks is useful.

Previously, in Implement a Functional Test, we learned how to tell BrowserTestBase to use the Standard installation profile in order to get our test passing, letting the Standard profile implicitly provide our dependencies. We mentioned that doing so probably wasn't the best decision and that we should explicitly declare those dependencies instead.

In this tutorial, we'll walk through how to explicitly declare our test's dependencies. When in doubt, it's generally considered a best practice to be as explicit about the dependencies of our tests as possible. By the end of this tutorial, you should be able to:

• Understand why we want to explicitly declare our dependencies.
• Determine what the dependencies really are and make a list of them.
• Implement each dependency in our list.
• Emerge with a thorough passing test.

In this tutorial, we'll walk through the basics of how to implement a functional test by extending Drupal's BrowserTestBase class. We'll assume you've already determined that you need to write a functional test and that you've Set up a Functional Test.

In this tutorial, we'll:

• Determine the specifications of the test.
• Walk through the behavior we want to test.
• Document our test in the test class.
• Implement the testing steps.
• Decide how to deal with dependencies (for now). (We'll go into details about handling test dependencies in Implement Drupal Functional Test Dependencies.)

Let's write somewhat strict unit tests in a Drupal module. By the end of this tutorial, you will be able to:

• Understand what makes a unit test different from other types of tests.
• Determine the specifications of a unit test.
• Use mocking to isolate units under test, and to force code flow to achieve high coverage.

We'll start out with a brief introduction to unit tests. Then we'll look at a contrived example of a Drupal controller class for illustration purposes. Next, we'll test two units of this controller class, each requiring different mock styles.

In this gentle introduction to testing, we'll walk through what testing is and why it's important to your project. Then we'll define some terms you'll be likely to see while working with tests so that we're all on the same page. After reading through this tutorial you'll understand enough of the basic vocabulary to get started running (and eventually writing) tests for your Drupal site.

The testing suite for the Drupalize.Me site uses a different strategy for functional JavaScript testing. We use a tool called Nightwatch.js that allows us to write our tests in JavaScript that runs commands against a web browser. This browser automation allows us to test the types of interactions that a typical user of our website might encounter. It also allows us to test JavaScript code using JavaScript, and execute our tests in different browsers. In this tutorial we'll take a look at how to set up Nightwatch.js, and what the syntax looks like for a couple of basic tests.

In order for Drupal to be able to locate and run the tests you create, the files need to be put in the correct place. In this tutorial, we'll take a look at the different types of test frameworks that are included along with core. We'll also see how Drupal expects our test files to be organized so that the test runners can find them.