Expose engines

By implementing the `engine` method just like in version 3

lib/Cake/Cache/Cache.php

@@ -616,4 +616,19 @@ public static function add($key, $value, $config = 'default') {
 		self::set(null, $config);
 		return $success;
 	}
+
+/**
+ * Fetch the engine attached to a specific configuration name.
+ *
+ * @param string $config Optional string configuration name to get an engine for. Defaults to 'default'.
+ * @return bool|CacheEngine False if the engine has not been initialized else the engine
+ */
+	public static function engine($config = 'default') {
+		if (self::isInitialized($config)) {
+			return self::$_engines[$config];
+		}
+
+		return false;
+	}
+
 }

lib/Cake/Test/Case/Cache/CacheTest.php

@@ -538,4 +538,64 @@ public function testAdd() {
 		$result = Cache::add('test_add_key', 'test data 2', 'default');
 		$this->assertFalse($result);
 	}
+
+/**
+ * Test engine method.
+ *
+ *  Success, default engine.
+ *
+ * @return void
+ */
+	public function testEngineSuccess() {
+		$actual = Cache::engine();
+		$this->assertIsA($actual, 'CacheEngine');
+
+		$actual = Cache::engine('default');
+		$this->assertIsA($actual, 'CacheEngine');
+	}
+
+/**
+ * Test engine method.
+ *
+ *  Success, memcached engine.
+ *
+ * @return void
+ */
+	public function testEngineSuccessMemcached() {
+		$this->skipIf(!class_exists('Memcached'), 'Memcached is not installed or configured properly.');
+
+		// @codingStandardsIgnoreStart
+		$socket = @fsockopen('127.0.0.1', 11211, $errno, $errstr, 1);
+		// @codingStandardsIgnoreEnd
+		$this->skipIf(!$socket, 'Memcached is not running.');
+		fclose($socket);
+
+		Cache::config('memcached', array(
+			'engine' => 'Memcached',
+			'prefix' => 'cake_',
+			'duration' => 3600
+		));
+
+		$actual = Cache::engine('memcached');
+		$this->assertTrue($actual->add('test_add_key', 'test data', 10));
+		$this->assertFalse($actual->add('test_add_key', 'test data', 10));
+		$this->assertTrue($actual->delete('test_add_key'));
+	}
+
+/**
+ * Test engine method.
+ *
+ *  Failure.
+ *
+ * @return void
+ */
+	public function testEngineFailure() {
+		$actual = Cache::engine('some_config_that_does_not_exist');
+		$this->assertFalse($actual);
+
+		Configure::write('Cache.disable', true);
+		$actual = Cache::engine();
+		$this->assertFalse($actual);
+	}
+
 }