Framework: Store one Factory instance per subclass

includes/framework/class-factory.php

@@ -15,11 +15,11 @@
 abstract class Factory {
 
 	/**
-	 * Container for the main instance of the class.
+	 * Container for the main instance of each factory subclass, keyed by class name.
 	 *
-	 * @property ?Model
+	 * @var array<class-string<static>, static>
 	 */
-	protected static $instance = null;
+	protected static $instances = array();
 
 	/**
 	 * Instantiates a model object.
@@ -33,15 +33,16 @@ abstract public function make( $args );
 	/**
 	 * Utility method to retrieve the main instance of the class.
 	 *
-	 * The instance will be created if it does not exist yet.
+	 * The instance will be created if it does not exist yet. Each subclass
+	 * has its own instance.
 	 *
-	 * @return Model The main instance.
+	 * @return static The main instance.
 	 */
 	public static function get_instance() {
-		if ( null === self::$instance ) {
-			self::$instance = new static();
+		if ( ! isset( self::$instances[ static::class ] ) ) {
+			self::$instances[ static::class ] = new static();
 		}
 
-		return self::$instance;
+		return self::$instances[ static::class ];
 	}
 }

tests/phpunit/tests/framework/test-factory.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace WP\Notifications\Tests;
+
+use WP\Notifications\Factory;
+
+/**
+ * @covers \WP\Notifications\Framework\Factory
+ */
+class Test_Framework_Factory extends TestCase {
+
+	/**
+	 * Should return an instance of the subclass it is called on.
+	 */
+	public function test_get_instance_returns_instance_of_called_class() {
+		$this->assertInstanceOf( Factory\Message::class, Factory\Message::get_instance() );
+		$this->assertInstanceOf( Factory\Notification::class, Factory\Notification::get_instance() );
+		$this->assertInstanceOf( Factory\Subscription::class, Factory\Subscription::get_instance() );
+	}
+
+	/**
+	 * Should not share one instance across factory subclasses.
+	 */
+	public function test_get_instance_is_distinct_per_subclass() {
+		$message      = Factory\Message::get_instance();
+		$notification = Factory\Notification::get_instance();
+		$subscription = Factory\Subscription::get_instance();
+
+		$this->assertNotSame( $message, $notification );
+		$this->assertNotSame( $message, $subscription );
+		$this->assertNotSame( $notification, $subscription );
+	}
+
+	/**
+	 * Should return the same instance on repeated calls for the same subclass.
+	 */
+	public function test_get_instance_is_singleton_per_subclass() {
+		$this->assertSame( Factory\Message::get_instance(), Factory\Message::get_instance() );
+		$this->assertSame( Factory\Notification::get_instance(), Factory\Notification::get_instance() );
+		$this->assertSame( Factory\Subscription::get_instance(), Factory\Subscription::get_instance() );
+	}
+}