Editing the WPGraphQL API can be tricky at times, even more so when dealing with a massive plugin like WooCommerce. Don't let this discourage you though, it's possible simplify this development process with some application of Test-Driven Development (TDD). Now if you've ever been told anything about TDD, it's probably that TDD doesn't always fit everyone's development process. Nonetheless, the argument I'm trying to make is here is that using TDD and following this guide, you'll learn how to make proper changes to the WPGraphQL/WooGraphQL schema as well as write code that you know works regardless of where the GraphQL request came from or where the WPGraphQL server is installed.

WPGraphQL and WooGraphQL both use the Codeception testing framework alongside the wp-browser module created by Luca Tumedei for running the automated test suite. We'll be using Codeception scaffolding to generate all the tedious test code, but this will not be an in-depth guide on either of these libraries. It's not required to process with this tutorial, but it's highly recommended that after finishing this tutorial you take a look at the documentation for both.

• Codeception
• wp-browser

Before we can begin testing we need a local WordPress installation. If you already have a local installation for development that you wish to use, make a backup database for testing and skip to Setting up Codeception. If you don't have a local installation or simply don't want to risk your local installation, you can use the scripts provided by WPGraphQL and WooGraphQL to create one for testing in a temporary directory.

Have PHP, MySQL or PostgreSQL, Composer, and WP-CLI installed as well as terminal/shell/command-line access.

1. Start by cloning WooGraphQL.

2. Open your terminal.

3. Copy the .env.dist to .env by execute the following in your terminal in the WooGraphQL root directory.

   cp .env.testing .env

4. Open the .env and update the second group of boxed environmental variables in the image below to match your machine setup. If you're on Windows (Not WSL) you'll have to set the first boxed group as well because by default the installation location is ./local/public within the plugin directory is used, and Windows does not support symlink/shortcuts being nested inside their destination.

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5. Last thing to do is run the WordPress testing environment install script in the terminal.

   composer install-test-env

This will create and configure a WordPress installation in a temporary directory for the purpose of testing.

Now that we have setup our testing environment, let's run the tests. To do this we will need to install the Codeception and the rest of our devDependencies

1. First run composer installTestEnv in the terminal.

2. Next copy the codeception.dist.yml to codeception.yml

   cp codeception.dist.yml codeception.yml

3. Open codeception.yml and make the following changes.

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Now you all set to run the tests locally.

Now we're ready to get started with testing. There is a small issue you may have with our testing environment. The WordPress installation we created doesn't support end-to-end (e2e) testing, however this won't be a problem. WPGraphQL is an API and most of the time you can get away with just ensuring that your query works, and WPGraphQL provides a few functions that will allow us to do just that.

Well, let's get started by running all the unit tests. Back in your terminal run the following:

vendor/bin/codecept run wpunit

If everything is how it should be you should get all passing tests.

This rest of this guide walk through creating a competent WPUnit test and implemented the functionality needed to ensure that test passed. For the most part everything used here can be used when making changes to WPGraphQL as well as many of the WPGraphQL extensions created by @jasonbahl, myself and the WPGraphQL community.

The functionality we'll be adding in the coming steps will be to add the Integer field itemCount on the Cart object type. To do this we'll be.

1. Generating a WPUnit test file Now typically for a feature so small it would be enough to update the first test in the CartQueriesTest class to include the desired itemCount field, however to the purpose of this guide we'll be creating a new test file named ItemCountTest.
2. Writing our test The name says it all.
3. Run the test expecting failure The purpose of this step will be used to introduce to WPGraphQL's Error Reporting and the codecept_debug function.
4. Implementing our changes This step will do some exploring into how WooGraphQL and WPGraphQL work behind the scenes, and diving in to some key components. After acquiring a grasp of WPGraphQL execution implementing the desired changes with be trivially.
5. Run test expecting success The final step will be to the ItemCountTest looking for success this time.

The PHP testing suite used by WPGraphQL and WooGraphQL is Codeception, but they don't manage the codeception/codeception in Composer. That is done by the lucatume/wp-browser package. This package, developed and maintained by theAverageDev Luca Tumedei, wp-browser is a suite of Codeception modules that provide tools designed specifically for testing WordPress sites, themes, and plugins on multiple levels. The lucatume/wp-browser package functions as a one-stop shop managing Codeception and all it's dependencies for WPGraphQL and many of it's extensions.

So having done everything above, and finally being ready for development, begin by generating the ItemCountTest test file with Codeception generate command. Run the following in your terminal from the project root directory

vendor/bin/codecept generate:wpunit wpunit "ItemCount"

This will generate a new test file at tests/wpunit/ItemCountTest.php. The generate is an easy-to-use tool of convience. You learn more about here.

The ItemCountTest.php file should be a familiar site to anyone whose used Codeception or PHPUnit (which Codeception is built on).

<?php

class ItemCountTest extends \Codeception\TestCase\WPTestCase
{

    public function setUp(): void {
        // before
        parent::setUp();

        // your set up methods here
    }

    public function tearDown(): void {
        // your tear down methods here

        // then
        parent::tearDown();
    }

    // tests
    public function testMe()
    {
    }
}

This functions execute before and after every function. The setUp() in particular is perfect place to create objects such posts, products, orders, etc to test with as well as set any WordPress options that maybe needed or interfere with the tests. The tearDown() is good for deleting things that Codeception and wp-browser miss, which isn't much so it not uncommon for the function to be left an empty stub.

There's also the wpSetUpBeforeClass( $factory ) and wpTearDownAfterClass( $factory ) that are run before all the tests, however their use-case is even move rare then tearDown() on account that these methods are static and don't have access to the same $this context as the setUp(), tearDown() or test*() function.

Class functions that are prefix with test are tests. These functions are run on isolation for the most part. Test function must be public access. The purpose of the test function is to confirm the correct data is provided by when requested. This is done using the Assert library provided by PHPUnit which is wrapped by the Codeception framework and used by will everything on top of it.

$this->assertEquals( array( 5 ), [ 5 ] );

Now that we've gone over the basic functions of a Unit test let's go ahead and modify it for a needs.

<?php

use Tests\WPGraphQL\WooCommerce\TestCase\WooGraphQLTestCase;

class ItemCountTest extends WooGraphQLTestCase {

    // tests
    public function testMe()
    {
    }
}

Here we'll be utilizing a WooGraphQLTestCase bundled in the WooGraphQL test environment. It extends the WPGraphQLTestCase class provided by the WPGraphQL TestCase library. Which was designed specifically for testing WPGraphQL responses.

Making changes to GraphQL API is always a rather top-down affair, meaning you'll have an idea of how you want the query to look before you have an idea of how you want the implementation to look. For example the query in relation to the changes we want to make will be as follows.

query {
    cart {
        contents {
            nodes {
                quantity
            }
        }
        itemCount
    }
}

Nothing special, but if you sent this query to the WPGraphQL server you'd get back.

{
  "errors": [
    {
      "message": "Cannot query field \"itemCount\" on type \"Cart\".",
      "extensions": {
        "category": "graphql"
      },
      "locations": [
        {
          "line": 8,
          "column": 5
        }
      ]
    }
  ],
}

Which shouldn't be surprising, in the next section we'll be taking this query and creating our test around it.

If you didn't already know, an itemCount field already exist. It just happens to be under the contents connection as a field you can access it like this.

query {
  cart { contents { itemCount } }
}

WooCommerce is a vast WordPress plugin with a lot moving parts and getting them all to play nice can be a daunting task. To address this the WooGraphQLTestCase class provides a number of factories for creating just the right scenario for testing our queries. In this guide you'll be expose to the cart and product factories, but there are quite a few. However documentation on them is pretty non-existant at the time of creation for this guide. Until this is rectified, it's recommended that you view factory files directly to get a general idea of what they are and their capabilities.

Let's finish begin writing out test by creating our scenario with the setUp(). Our scenario for this is test is rather simple, our query just need some products and those products have to be in the cart. Using product and cart helpers we can do this in a few lines of code.

public function testMe() {
    // Our scenario
    $products = [
        [
            'product_id' => $this->factory->product->createSimple(),
            'quantity'   => 1,
        ],
        [
            'product_id' => $this->factory->product->createSimple(),
            'quantity'   => 1,
        ],
        [
            'product_id' => $this->factory->product->createSimple(),
            'quantity'   => 2,
        ],
        [
            'product_id' => $this->factory->product->createSimple(),
            'quantity'   => 3,
        ],
    ];

    $this->factory->cart->add( ...$products );
}

And that's it, scenario created. You maybe confused, but we'll break it down.

$products = [
    [
        'product_id' => $this->factory->product->createSimple(),
        'quantity'   => 1,
    ],
    [
        'product_id' => $this->factory->product->createSimple(),
        'quantity'   => 1,
    ],
    [
        'product_id' => $this->factory->product->createSimple(),
        'quantity'   => 2,
    ],
    [
        'product_id' => $this->factory->product->createSimple(),
        'quantity'   => 3,
    ],
];

The $product array holds the product_ids and quantitys of products being add to our cart. createSimple( $args = array() ) creates a new simple product with a random name and price and returns the product_id of the newly created product. There are createExternal( $args = array() ), createGrouped( $args = array() ) and createVariable( $args = array() ), as well as many more create functions for creating other objects related to products.

$this->factory->cart->add( ...$products );

And finally, you have probably figured out that this adds the products in $products to the cart. cart factory functions as a glorified wrapper for the WC()->cart instance with a extra features for testing.

Now that our scenario is set. Let's get to are test. We'll start by change the name of the test to testItemCountField and assign our query to a string variable.

public function testItemCountField() {
    // Our scenario
    ...

    $query = '
        query {
            cart {
                contents {
                    nodes {
                        quantity
                    }
                }
                itemCount
            }
        }
    ';
}

Simple enough, next we'll run our query through WPGraphQL using graphql( $request_data = [] ).

public function testItemCountField() {
    // Our scenario
    ...

    $response = $this->graphql( [ 'query' => $query ] );
}

$this->graphql() is a simple wrapper for the graphql() function provided by WPGraphQL. It will process a GraphQL request and return the results as an associative array. This makes it a great tool for testing our queries.

Another this about the wrapper is if the --debug flag is passed when using Codeception's run command, the response from graphql() is pretty printed to the console. Its use here is great because when we run our test later in debug mode we'll know exactly what WPGraphQL is returning for our query.

The last step in our test is to confirm the we received the correct values for our itemCount field.

public function testItemCountField() {
    // Our scenario
    ...

    $expected = [
        $this->expectedField(
            'cart.itemCount',
            array_sum( array_column( $products, 'quantity' ) )
        ),
    ];
    $this->assertQuerySuccessful( $response, $expected );
}

And that's our test. You notice we're only testing our new field with the expectedField function and nothing else the query may have returned. That's the primary purpose of WPGraphQL TestCase. It provides functions like expectedField and expectedNode to isolate and test the parts of the query you care about and ignore everything else. This will save you from the hell that comes from testing groups of nodes that come in an order you've not predicted in your test.

<?php

use Tests\WPGraphQL\WooCommerce\TestCase\WooGraphQLTestCase;

class ItemCountTest extends WooGraphQLTestCase {

    // tests
    public function testItemCountField() {
        // Our scenario
        $products = [
            [
                'product_id' => $this->factory->product->createSimple(),
                'quantity'   => 1,
            ],
            [
                'product_id' => $this->factory->product->createSimple(),
                'quantity'   => 1,
            ],
            [
                'product_id' => $this->factory->product->createSimple(),
                'quantity'   => 2,
            ],
            [
                'product_id' => $this->factory->product->createSimple(),
                'quantity'   => 3,
            ],
        ];

        $this->factory->cart->add( ...$products );

        $query = '
            query {
                cart {
                    contents {
                        nodes {
                            quantity
                        }
                    }
                    itemCount
                }
            }
        ';

        $response = $this->graphql( [ 'query' => $query ] );
        $expected = [
            $this->expectedField(
                'cart.itemCount',
                array_sum( array_column( $products, 'quantity' ) )
            ),
        ];
        $this->assertQuerySuccessful( $response, $expected );
    }
}

Now that the test is created, we will run it expecting failure and using the --debug flag.

vendor/bin/codecept run wpunit ItemCountTest --debug

Running this statement in the terminal will make Codeception run just the ItemCountTest in debug mode. This way we can see exactly WPGraphQL returns for our query.

Running the test will result in the error above. Cannot query field "itemCount" on type "Cart". The error is quite easy to understand. We cannot query a field that doesn't yet exist.

Before when jump into the code, lets discuss how WPGraphQL and WooGraphQL process requests.

When a request is made to Wordpress, during the after_setup_theme action WPGraphQL initializes the Router class which is in-charge of determining whether the request is a GraphQL request and acting accordingly. If the request is a GraphQL request, a Request class instance is created. It's job is to load the schema and process the request. The first part of loading the schema and our focal point for purpose is the initialization of the TypeRegistry and specific the execution of graphql_register_types action. This hook serves the purpose of providing a location to register types not defined by WPGraphQL.

WooGraphQL uses graphql_register_types to register WooCommerce specific types. If you're familiar WordPress, you're most like familiar with Custom Post-types (CPTs) the core data object used by WordPress. If you're not too familiar with WooCommerce, (or even if you are), you maybe wondering why the CPTs in WooCommerce have such a different schema shape the CPTs defined by WPGraphQL. This due to the fact the WooCommerce wraps it's CPT objects, (WP_Post), in data stores objects. This data stores provide decorator functionality that is widely used by WooCommerce extension. WooGraphQL uses data stores as the source for it CPT schema shapes. All other types like the cart and shipping zones are sourced by custom data objects saved in custom databases, and accessed using WooCommerce built-in functionality.

Now to implement our changes we simply need to register our itemCount field to the Cart object type.

register_graphql_field(
    'Cart',
    'itemCount',
    [
        'type'        => 'Int',
        'description' => __( 'Total number of items in the cart.', 'wp-graphql-woocommerce' ),
        'resolve'     => function( \WC_Cart $source ) {
            $items = $source->get_cart();
            if ( empty( $items ) ) {
                return 0;
            }

            return array_sum( array_column( $items, 'quantity' ) );
        },
    ],
);

Simple enough, right. Now we can slap this at the end of the TypeRegistry and it would fine, however for a pull request that wouldn't work. So let's include this the inside the register_graphql_object_type() call for the Cart type with the rest of Cart fields. This call can be found in Cart_Type::register_cart() in includes/type/object/class-cart-type.php.

    /**
     * Registers Cart type
     */
    public static function register_cart() {
        register_graphql_object_type(
            'Cart',
            array(
                'description' => __( 'The cart object', 'wp-graphql-woocommerce' ),
                'fields'      => [
                    ... // Other cart fields
                    'itemCount' => [
                        'type'        => 'Int',
                        'description' => __( 'Total number of items in the cart.', 'wp-graphql-woocommerce' ),
                        'resolve'     => function( \WC_Cart $source ) {
                            $items = $source->get_cart();
                            if ( empty( $items ) ) {
                                return 0;
                            }

                            return array_sum( array_column( $items, 'quantity' ) );
                        },
                    ],
                ],
            )
        );
    }

And 💥! Changes made. Let's run our test!!

Now if you re-run vendor/bin/codecept run wpunit ItemCountTest

And we have passed, and if we want to see our query response use the --debug flag

If you have already, you should at least take a look at the following

• Documentation on extending WPGraphQL. Here.
• WooCommerce REST API Docs, seeing as it has been and continues to be the base template for the WooGraphQL schema.

If you plan on contributing you should see the following as both WPGraphQL and WooGraphQL uses them.

• Codeception Docs
• wp-browser Docs