class DiscoveryTestBase

abstract class DiscoveryTestBase extends KernelTestBase {
    
    /**
     * The discovery component to test.
     *
     * @var \Drupal\Component\Plugin\Discovery\DiscoveryInterface
     */
    protected $discovery;
    
    /**
     * The plugin definitions the discovery component is expected to discover.
     *
     * @var array
     */
    protected $expectedDefinitions;
    
    /**
     * An empty discovery component.
     *
     * This will be tested to ensure that the case where no plugin information is
     * found, is handled correctly.
     *
     * @var \Drupal\Component\Plugin\Discovery\DiscoveryInterface
     */
    protected $emptyDiscovery;
    
    /**
     * Tests getDefinitions() and getDefinition().
     */
    public function testDiscoveryInterface() : void {
        // Ensure that getDefinitions() returns the expected definitions.
        // For the arrays to be identical (instead of only equal), they must be
        // sorted equally, which seems unnecessary here.
        // The discovered definitions may contain circular references; use a custom
        // assertion message to prevent var_export() from getting called.
        $this->assertEquals($this->expectedDefinitions, $this->discovery
            ->getDefinitions(), 'Expected definitions found.');
        // Ensure that getDefinition() returns the expected definition.
        foreach ($this->expectedDefinitions as $id => $definition) {
            $this->assertDefinitionIdentical($this->discovery
                ->getDefinition($id), $definition);
        }
        // Ensure that an empty array is returned if no plugin definitions are found.
        $this->assertSame([], $this->emptyDiscovery
            ->getDefinitions(), 'array() returned if no plugin definitions are found.');
        // Ensure that NULL is returned as the definition of a non-existing plugin.
        $this->assertNull($this->emptyDiscovery
            ->getDefinition('non_existing', FALSE), 'NULL returned as the definition of a non-existing plugin.');
    }
    
    /**
     * Asserts a definition against an expected definition.
     *
     * Converts any instances of \Drupal\Core\Annotation\Translation to a string.
     *
     * @param array $definition
     *   The definition to test.
     * @param array $expected_definition
     *   The expected definition to test against.
     */
    protected function assertDefinitionIdentical(array $definition, array $expected_definition) {
        $func = function (&$item) {
            if ($item instanceof TranslatableMarkup) {
                $item = (string) $item;
            }
        };
        array_walk_recursive($definition, $func);
        array_walk_recursive($expected_definition, $func);
        $this->assertSame($expected_definition, $definition);
    }

}