VariationCacheTest.php

<?php

declare (strict_types=1);
namespace Drupal\Tests\Core\Cache;

use Drupal\Component\Datetime\Time;
use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Cache\CacheRedirect;
use Drupal\Core\Cache\Context\CacheContextsManager;
use Drupal\Core\Cache\Context\ContextCacheKeys;
use Drupal\Core\Cache\MemoryBackend;
use Drupal\Core\Cache\VariationCache;
use Drupal\Tests\UnitTestCase;
use Prophecy\Argument;
use Symfony\Component\HttpFoundation\RequestStack;

/**
 * @coversDefaultClass \Drupal\Core\Cache\VariationCache
 * @group Cache
 */
class VariationCacheTest extends UnitTestCase {
    
    /**
     * The prophesized request stack.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack|\Prophecy\Prophecy\ProphecyInterface
     */
    protected $requestStack;
    
    /**
     * The backend used by the variation cache.
     *
     * @var \Drupal\Core\Cache\MemoryBackend
     */
    protected $memoryBackend;
    
    /**
     * The prophesized cache contexts manager.
     *
     * @var \Drupal\Core\Cache\Context\CacheContextsManager|\Prophecy\Prophecy\ProphecyInterface
     */
    protected $cacheContextsManager;
    
    /**
     * The variation cache instance.
     *
     * @var \Drupal\Core\Cache\VariationCacheInterface
     */
    protected $variationCache;
    
    /**
     * The cache keys this test will store things under.
     *
     * @var string[]
     */
    protected $cacheKeys = [
        'your',
        'housing',
        'situation',
    ];
    
    /**
     * The cache ID for the cache keys, without taking contexts into account.
     *
     * @var string
     */
    protected $cacheIdBase = 'your:housing:situation';
    
    /**
     * The simulated current user's housing type.
     *
     * For use in tests with cache contexts.
     *
     * @var string
     */
    protected $housingType;
    
    /**
     * The cacheability for something that only varies per housing type.
     *
     * @var \Drupal\Core\Cache\CacheableMetadata
     */
    protected $housingTypeCacheability;
    
    /**
     * The simulated current user's garden type.
     *
     * For use in tests with cache contexts.
     *
     * @var string
     */
    protected $gardenType;
    
    /**
     * The cacheability for something that varies per housing and garden type.
     *
     * @var \Drupal\Core\Cache\CacheableMetadata
     */
    protected $gardenTypeCacheability;
    
    /**
     * The simulated current user's house's orientation.
     *
     * For use in tests with cache contexts.
     *
     * @var string
     */
    protected $houseOrientation;
    
    /**
     * The cacheability for varying per housing, garden and orientation.
     *
     * @var \Drupal\Core\Cache\CacheableMetadata
     */
    protected $houseOrientationCacheability;
    
    /**
     * The simulated current user's solar panel type.
     *
     * For use in tests with cache contexts.
     *
     * @var string
     */
    protected $solarType;
    
    /**
     * {@inheritdoc}
     */
    protected function setUp() : void {
        parent::setUp();
        $this->requestStack = $this->prophesize(RequestStack::class);
        $this->memoryBackend = new MemoryBackend(new Time());
        $this->cacheContextsManager = $this->prophesize(CacheContextsManager::class);
        $housing_type =& $this->housingType;
        $garden_type =& $this->gardenType;
        $house_orientation =& $this->houseOrientation;
        $solar_type =& $this->solarType;
        $this->cacheContextsManager
            ->convertTokensToKeys(Argument::any())
            ->will(function ($args) use (&$housing_type, &$garden_type, &$house_orientation, &$solar_type) {
            $keys = [];
            foreach ($args[0] as $context_id) {
                switch ($context_id) {
                    case 'house.type':
                        $keys[] = "ht.{$housing_type}";
                        break;
                    case 'garden.type':
                        $keys[] = "gt.{$garden_type}";
                        break;
                    case 'house.orientation':
                        $keys[] = "ho.{$house_orientation}";
                        break;
                    case 'solar.type':
                        $keys[] = "st.{$solar_type}";
                        break;
                    default:
                        $keys[] = $context_id;
                }
            }
            return new ContextCacheKeys($keys);
        });
        $this->variationCache = new VariationCache($this->requestStack
            ->reveal(), $this->memoryBackend, $this->cacheContextsManager
            ->reveal());
        $this->housingTypeCacheability = (new CacheableMetadata())->setCacheTags([
            'foo',
        ])
            ->setCacheContexts([
            'house.type',
        ]);
        $this->gardenTypeCacheability = (new CacheableMetadata())->setCacheTags([
            'bar',
        ])
            ->setCacheContexts([
            'house.type',
            'garden.type',
        ]);
        $this->houseOrientationCacheability = (new CacheableMetadata())->setCacheTags([
            'baz',
        ])
            ->setCacheContexts([
            'house.type',
            'garden.type',
            'house.orientation',
        ]);
    }
    
    /**
     * Tests a cache item that has no variations.
     *
     * @covers ::get
     * @covers ::set
     */
    public function testNoVariations() : void {
        $data = 'You have a nice house!';
        $cacheability = (new CacheableMetadata())->setCacheTags([
            'bar',
            'foo',
        ]);
        $initial_cacheability = (new CacheableMetadata())->setCacheTags([
            'foo',
        ]);
        $this->setVariationCacheItem($data, $cacheability, $initial_cacheability);
        $this->assertVariationCacheItem($data, $cacheability, $initial_cacheability);
    }
    
    /**
     * Tests a cache item that only ever varies by one context.
     *
     * @covers ::get
     * @covers ::set
     */
    public function testSingleVariation() : void {
        $cacheability = $this->housingTypeCacheability;
        $house_data = [
            'apartment' => 'You have a nice apartment',
            'house' => 'You have a nice house',
        ];
        foreach ($house_data as $housing_type => $data) {
            $this->housingType = $housing_type;
            $this->assertVariationCacheMiss($cacheability);
            $this->setVariationCacheItem($data, $cacheability, $cacheability);
            $this->assertVariationCacheItem($data, $cacheability, $cacheability);
            $this->assertCacheBackendItem("{$this->cacheIdBase}:ht.{$housing_type}", $data, $cacheability);
        }
    }
    
    /**
     * Tests a cache item that has nested variations.
     *
     * @covers ::get
     * @covers ::set
     */
    public function testNestedVariations() : void {
        // We are running this scenario in the best possible outcome: The redirects
        // are stored in expanding order, meaning the simplest one is stored first
        // and the nested ones are stored in subsequent ::set() calls. This means no
        // self-healing takes place where overly specific redirects are overwritten
        // with simpler ones.
        $possible_outcomes = [
            'apartment' => 'You have a nice apartment!',
            'house|no-garden' => 'You have a nice house!',
            'house|garden|east' => 'You have a nice house with an east-facing garden!',
            'house|garden|south' => 'You have a nice house with a south-facing garden!',
            'house|garden|west' => 'You have a nice house with a west-facing garden!',
            'house|garden|north' => 'You have a nice house with a north-facing garden!',
        ];
        foreach ($possible_outcomes as $cache_context_values => $data) {
            [
                $this->housingType,
                $this->gardenType,
                $this->houseOrientation,
            ] = explode('|', $cache_context_values . '||');
            $cacheability = $this->housingTypeCacheability;
            if (!empty($this->houseOrientation)) {
                $cacheability = $this->houseOrientationCacheability;
            }
            elseif (!empty($this->gardenType)) {
                $cacheability = $this->gardenTypeCacheability;
            }
            $this->assertVariationCacheMiss($this->housingTypeCacheability);
            $this->setVariationCacheItem($data, $cacheability, $this->housingTypeCacheability);
            $this->assertVariationCacheItem($data, $cacheability, $this->housingTypeCacheability);
            $cache_id_parts = [
                "ht.{$this->housingType}",
            ];
            if (!empty($this->gardenType)) {
                $this->assertCacheBackendItem($this->getSortedCacheId($cache_id_parts), new CacheRedirect($this->gardenTypeCacheability));
                $cache_id_parts[] = "gt.{$this->gardenType}";
            }
            if (!empty($this->houseOrientation)) {
                $this->assertCacheBackendItem($this->getSortedCacheId($cache_id_parts), new CacheRedirect($this->houseOrientationCacheability));
                $cache_id_parts[] = "ho.{$this->houseOrientation}";
            }
            $this->assertCacheBackendItem($this->getSortedCacheId($cache_id_parts), $data, $cacheability);
        }
    }
    
    /**
     * Tests a cache item that has nested variations that trigger self-healing.
     *
     * @covers ::get
     * @covers ::set
     *
     * @depends testNestedVariations
     */
    public function testNestedVariationsSelfHealing() : void {
        // This is the worst possible scenario: A very specific item was stored
        // first, followed by a less specific one. This means an overly specific
        // cache redirect was stored that needs to be dumbed down. After this
        // process, the first ::get() for the more specific item will fail as we
        // have effectively destroyed the path to said item. Setting an item of the
        // same specificity will restore the path for all items of said specificity.
        $cache_id_parts = [
            'ht.house',
        ];
        $possible_outcomes = [
            'house|garden|east' => 'You have a nice house with an east-facing garden!',
            'house|garden|south' => 'You have a nice house with a south-facing garden!',
            'house|garden|west' => 'You have a nice house with a west-facing garden!',
            'house|garden|north' => 'You have a nice house with a north-facing garden!',
        ];
        foreach ($possible_outcomes as $cache_context_values => $data) {
            [
                $this->housingType,
                $this->gardenType,
                $this->houseOrientation,
            ] = explode('|', $cache_context_values . '||');
            $this->setVariationCacheItem($data, $this->houseOrientationCacheability, $this->housingTypeCacheability);
        }
        // Verify that the overly specific redirect is stored at the first possible
        // redirect location, i.e.: The base cache ID.
        $this->assertCacheBackendItem($this->getSortedCacheId($cache_id_parts), new CacheRedirect($this->houseOrientationCacheability));
        // Store a simpler variation and verify that the first cache redirect is now
        // the one redirecting to the simplest known outcome.
        [
            $this->housingType,
            $this->gardenType,
            $this->houseOrientation,
        ] = [
            'house',
            'no-garden',
            NULL,
        ];
        $this->setVariationCacheItem('You have a nice house', $this->gardenTypeCacheability, $this->housingTypeCacheability);
        $this->assertCacheBackendItem($this->getSortedCacheId($cache_id_parts), new CacheRedirect($this->gardenTypeCacheability));
        // Verify that the previously set outcomes are all inaccessible now.
        foreach ($possible_outcomes as $cache_context_values => $data) {
            [
                $this->housingType,
                $this->gardenType,
                $this->houseOrientation,
            ] = explode('|', $cache_context_values . '||');
            $this->assertVariationCacheMiss($this->housingTypeCacheability);
        }
        // Set at least one more specific item in the cache again.
        $this->setVariationCacheItem($data, $this->houseOrientationCacheability, $this->housingTypeCacheability);
        // Verify that the previously set outcomes are all accessible again.
        foreach ($possible_outcomes as $cache_context_values => $data) {
            [
                $this->housingType,
                $this->gardenType,
                $this->houseOrientation,
            ] = explode('|', $cache_context_values . '||');
            $this->assertVariationCacheItem($data, $this->houseOrientationCacheability, $this->housingTypeCacheability);
        }
        // Verify that the more specific cache redirect is now stored one step after
        // the less specific one.
        $cache_id_parts[] = 'gt.garden';
        $this->assertCacheBackendItem($this->getSortedCacheId($cache_id_parts), new CacheRedirect($this->houseOrientationCacheability));
    }
    
    /**
     * Tests self-healing for a cache item that has split variations.
     *
     * @covers ::get
     * @covers ::set
     */
    public function testSplitVariationsSelfHealing() : void {
        // This is an edge case. Something varies by AB where some values of B
        // trigger the whole to vary by either C, D or nothing extra. But due to an
        // unfortunate series of requests, only ABC and ABD variations were cached.
        //
        // In this case, the cache should be smart enough to generate a redirect for
        // AB, followed by redirects for ABC and ABD.
        //
        // For the sake of this test, we'll vary by housing and orientation, but:
        // - Only vary by garden type for south-facing houses.
        // - Only vary by solar panel type for north-facing houses.
        $this->housingType = 'house';
        $this->gardenType = 'garden';
        $this->solarType = 'solar';
        $initial_cacheability = (new CacheableMetadata())->setCacheTags([
            'foo',
        ])
            ->setCacheContexts([
            'house.type',
        ]);
        $south_cacheability = (new CacheableMetadata())->setCacheTags([
            'foo',
        ])
            ->setCacheContexts([
            'house.type',
            'house.orientation',
            'garden.type',
        ]);
        $north_cacheability = (new CacheableMetadata())->setCacheTags([
            'foo',
        ])
            ->setCacheContexts([
            'house.type',
            'house.orientation',
            'solar.type',
        ]);
        $common_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'house.orientation',
        ]);
        // Calculate the cache IDs once beforehand for readability.
        $cache_id = $this->getSortedCacheId([
            'ht.house',
        ]);
        $cache_id_north = $this->getSortedCacheId([
            'ht.house',
            'ho.north',
        ]);
        $cache_id_south = $this->getSortedCacheId([
            'ht.house',
            'ho.south',
        ]);
        // Set the first scenario.
        $this->houseOrientation = 'south';
        $this->setVariationCacheItem('You have a south-facing house with a garden!', $south_cacheability, $initial_cacheability);
        // Verify that the overly specific redirect is stored at the first possible
        // redirect location, i.e.: The base cache ID.
        $this->assertCacheBackendItem($cache_id, new CacheRedirect($south_cacheability));
        // Store a split variation, and verify that the common contexts are now used
        // for the first cache redirect and the actual contexts for the next step of
        // the redirect chain.
        $this->houseOrientation = 'north';
        $this->setVariationCacheItem('You have a north-facing house with solar panels!', $north_cacheability, $initial_cacheability);
        $this->assertCacheBackendItem($cache_id, new CacheRedirect($common_cacheability));
        $this->assertCacheBackendItem($cache_id_north, new CacheRedirect($north_cacheability));
        // Verify that the initially set scenario is inaccessible now.
        $this->houseOrientation = 'south';
        $this->assertVariationCacheMiss($initial_cacheability);
        // Reset the initial scenario and verify that its redirects are accessible.
        $this->setVariationCacheItem('You have a south-facing house with a garden!', $south_cacheability, $initial_cacheability);
        $this->assertCacheBackendItem($cache_id, new CacheRedirect($common_cacheability));
        $this->assertCacheBackendItem($cache_id_south, new CacheRedirect($south_cacheability));
        // Double-check that the split scenario redirects are left untouched.
        $this->houseOrientation = 'north';
        $this->assertCacheBackendItem($cache_id, new CacheRedirect($common_cacheability));
        $this->assertCacheBackendItem($cache_id_north, new CacheRedirect($north_cacheability));
    }
    
    /**
     * Tests exception for a cache item that has incomplete variations.
     *
     * @covers ::get
     * @covers ::set
     */
    public function testIncompleteVariationsException() : void {
        // This should never happen. When someone first stores something in the
        // cache using context A and then tries to store something using context B,
        // something is wrong. There should always be at least one shared context at
        // the top level or else the cache cannot do its job.
        $this->expectException(\LogicException::class);
        $this->expectExceptionMessage("The complete set of cache contexts for a variation cache item must contain all of the initial cache contexts, missing: garden.type.");
        $this->housingType = 'house';
        $house_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
        ]);
        $this->gardenType = 'garden';
        $garden_cacheability = (new CacheableMetadata())->setCacheContexts([
            'garden.type',
        ]);
        $this->setVariationCacheItem('You have a nice garden!', $garden_cacheability, $garden_cacheability);
        $this->setVariationCacheItem('You have a nice house!', $house_cacheability, $garden_cacheability);
    }
    
    /**
     * Tests exception for a cache item that has an incomplete redirect.
     *
     * @covers ::get
     * @covers ::set
     */
    public function testIncompleteRedirectException() : void {
        // @todo Remove in Drupal 12.0.0. For more information, see:
        //   https://www.drupal.org/project/drupal/issues/3468921
        set_error_handler(static function (int $errno, string $errstr) : never {
            throw new \LogicException($errstr, $errno);
        }, E_USER_WARNING);
        // This should never happen. When we have a cache redirect at address A,
        // pointing to 'A,B:foo' and then someone tries to store a cache redirect at
        // A pointing to 'A,B', something is wrong. The cache contexts leading up to
        // a cache redirect should always be present on the redirect itself. In this
        // example, the final cache redirect should be for 'A,B:foo,B'.
        $this->expectException(\LogicException::class);
        $this->expectExceptionMessage('Trying to overwrite a cache redirect with one that has nothing in common, old one at address "house.type" was pointing to "garden.type:zen", new one points to "garden.type".');
        $this->housingType = 'house';
        $house_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
        ]);
        $this->gardenType = '1';
        $calculated_garden_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type:zen',
        ]);
        $this->setVariationCacheItem('You have a house with zen garden!', $calculated_garden_cacheability, $house_cacheability);
        $this->gardenType = 'baroque garden';
        $garden_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type',
        ]);
        try {
            $this->setVariationCacheItem('You have a house with a baroque garden!', $garden_cacheability, $house_cacheability);
        } finally {
            restore_error_handler();
        }
    }
    
    /**
     * Tests exception for a cache item that has incompatible cache redirects.
     *
     * @covers ::get
     * @covers ::set
     */
    public function testIncompatibleRedirectsException() : void {
        // @todo Remove in Drupal 12.0.0. For more information, see:
        //   https://www.drupal.org/project/drupal/issues/3468921
        set_error_handler(static function (int $errno, string $errstr) : never {
            throw new \LogicException($errstr, $errno);
        }, E_USER_WARNING);
        // This should never happen. When someone first triggers the storing of a
        // redirect using context A and then tries to store another redirect in the
        // same spot using context B, something is wrong. The cache contexts of all
        // previous redirects should always be present on the next redirect or item
        // you're trying to store.
        $this->expectException(\LogicException::class);
        $this->expectExceptionMessage('Trying to overwrite a cache redirect with one that has nothing in common, old one at address "house.type" was pointing to "garden.type", new one points to "house.orientation".');
        $this->housingType = 'house';
        $house_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
        ]);
        $this->gardenType = 'garden';
        $garden_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type',
        ]);
        $this->houseOrientation = 'north';
        $orientation_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'house.orientation',
        ]);
        $this->setVariationCacheItem('You have a nice house with a garden!', $garden_cacheability, $house_cacheability);
        try {
            $this->setVariationCacheItem('You have a nice north-facing house!', $orientation_cacheability, $house_cacheability);
        } finally {
            restore_error_handler();
        }
    }
    
    /**
     * Tests the same as above, but with more redirects.
     *
     * @covers ::get
     * @covers ::set
     *
     * @depends testIncompatibleRedirectsException
     */
    public function testIncompatibleChainedRedirectsException() : void {
        // @todo Remove in Drupal 12.0.0. For more information, see:
        //   https://www.drupal.org/project/drupal/issues/3468921
        set_error_handler(static function (int $errno, string $errstr) : never {
            throw new \LogicException($errstr, $errno);
        }, E_USER_WARNING);
        $this->expectException(\LogicException::class);
        $this->expectExceptionMessage('Trying to overwrite a cache redirect with one that has nothing in common, old one at address "house.type, garden.type" was pointing to "house.orientation", new one points to "solar.type".');
        $this->housingType = 'house';
        $house_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
        ]);
        $this->gardenType = 'no-garden';
        $garden_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type',
        ]);
        // This should set a redirect at ht.house specifying garden.type. So the
        // redirects below should find this redirect to be fine before getting to
        // the problematic one.
        $this->setVariationCacheItem('You have a nice house with no garden!', $garden_cacheability, $house_cacheability);
        $this->gardenType = 'garden';
        $this->houseOrientation = 'north';
        $orientation_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type',
            'house.orientation',
        ]);
        $this->solarType = 'solar';
        $solar_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type',
            'solar.type',
        ]);
        $this->setVariationCacheItem('You have a nice north-facing house with a garden!', $orientation_cacheability, $house_cacheability);
        try {
            $this->setVariationCacheItem('You have a nice house with solar panels and a garden!', $solar_cacheability, $house_cacheability);
        } finally {
            restore_error_handler();
        }
    }
    
    /**
     * Tests the same as above, but even more complex.
     *
     * @covers ::get
     * @covers ::set
     *
     * @depends testIncompatibleChainedRedirectsException
     */
    public function testIncompatibleChainedRedirectsComplexException() : void {
        // @todo Remove in Drupal 12.0.0. For more information, see:
        //   https://www.drupal.org/project/drupal/issues/3468921
        set_error_handler(static function (int $errno, string $errstr) : never {
            throw new \LogicException($errstr, $errno);
        }, E_USER_WARNING);
        $this->expectException(\LogicException::class);
        $this->expectExceptionMessage('Trying to overwrite a cache redirect with one that has nothing in common, old one at address "house.type, garden.type" was pointing to "house.orientation", new one points to "solar.type".');
        $this->housingType = 'house';
        $house_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
        ]);
        $this->gardenType = 'garden';
        $this->houseOrientation = 'north';
        $orientation_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type',
            'house.orientation',
        ]);
        $this->solarType = 'solar';
        $solar_cacheability = (new CacheableMetadata())->setCacheContexts([
            'house.type',
            'garden.type',
            'solar.type',
        ]);
        // This time, nothing primes the redirects so the first set will create a
        // redirect at ht.house, pointing to house.type, garden.type and solar.type.
        $this->setVariationCacheItem('You have a nice house with solar panels and a garden!', $solar_cacheability, $house_cacheability);
        // The second set will try to store a redirect at ht.house, pointing to
        // house.type, garden.type and house.orientation. This will trigger the
        // creation of a common redirect at ht.house, pointing to garden.type.
        $this->setVariationCacheItem('You have a nice north-facing house with a garden!', $orientation_cacheability, $house_cacheability);
        // Now we arrive at the same scenario as the test above. We have a redirect
        // chain at house.type of garden.type and finally house.orientation, but are
        // trying to set solar.type at that last address.
        try {
            $this->setVariationCacheItem('You have a nice house with solar panels and a garden!', $solar_cacheability, $house_cacheability);
        } finally {
            restore_error_handler();
        }
    }
    
    /**
     * Creates the sorted cache ID from cache ID parts.
     *
     * When core optimizes cache contexts it returns the keys alphabetically. To
     * make testing easier, we replicate said sorting here.
     *
     * @param string[] $cache_id_parts
     *   The parts to add to the base cache ID, will be sorted.
     *
     * @return string
     *   The correct cache ID.
     */
    protected function getSortedCacheId($cache_id_parts) : string {
        sort($cache_id_parts);
        array_unshift($cache_id_parts, $this->cacheIdBase);
        return implode(':', $cache_id_parts);
    }
    
    /**
     * Stores an item in the variation cache.
     *
     * @param mixed $data
     *   The data that should be stored.
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   The cacheability that should be used.
     * @param \Drupal\Core\Cache\CacheableMetadata $initial_cacheability
     *   The initial cacheability that should be used.
     */
    protected function setVariationCacheItem($data, CacheableMetadata $cacheability, CacheableMetadata $initial_cacheability) : void {
        $this->variationCache
            ->set($this->cacheKeys, $data, $cacheability, $initial_cacheability);
    }
    
    /**
     * Asserts that an item was properly stored in the variation cache.
     *
     * @param mixed $data
     *   The data that should have been stored.
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   The cacheability that should have been used.
     * @param \Drupal\Core\Cache\CacheableMetadata $initial_cacheability
     *   The initial cacheability that should be used.
     */
    protected function assertVariationCacheItem($data, CacheableMetadata $cacheability, CacheableMetadata $initial_cacheability) : void {
        $cache_item = $this->variationCache
            ->get($this->cacheKeys, $initial_cacheability);
        $this->assertNotFalse($cache_item, 'Variable data was stored and retrieved successfully.');
        $this->assertEquals($data, $cache_item->data, 'Variable cache item contains the right data.');
        $this->assertSame($cacheability->getCacheTags(), $cache_item->tags, 'Variable cache item uses the right cache tags.');
    }
    
    /**
     * Asserts that an item could not be retrieved from the variation cache.
     *
     * @param \Drupal\Core\Cache\CacheableMetadata $initial_cacheability
     *   The initial cacheability that should be used.
     */
    protected function assertVariationCacheMiss(CacheableMetadata $initial_cacheability) : void {
        $this->assertFalse($this->variationCache
            ->get($this->cacheKeys, $initial_cacheability), 'Nothing could be retrieved for the active cache contexts.');
    }
    
    /**
     * Asserts that an item was properly stored in the cache backend.
     *
     * @param string $cid
     *   The cache ID that should have been used.
     * @param mixed $data
     *   The data that should have been stored.
     * @param \Drupal\Core\Cache\CacheableMetadata|null $cacheability
     *   (optional) The cacheability that should have been used. Does not apply
     *   when checking for cache redirects.
     */
    protected function assertCacheBackendItem(string $cid, $data, ?CacheableMetadata $cacheability = NULL) : void {
        $cache_backend_item = $this->memoryBackend
            ->get($cid);
        $this->assertNotFalse($cache_backend_item, 'The data was stored and retrieved successfully.');
        $this->assertEquals($data, $cache_backend_item->data, 'Cache item contains the right data.');
        if ($data instanceof CacheRedirect) {
            $this->assertSame([], $cache_backend_item->tags, 'A cache redirect does not use cache tags.');
            $this->assertSame(-1, $cache_backend_item->expire, 'A cache redirect is stored indefinitely.');
        }
        else {
            $this->assertSame($cacheability->getCacheTags(), $cache_backend_item->tags, 'Cache item uses the right cache tags.');
        }
    }

}