docs: add namespace App\Libraries to sample code

Author: kenjis

user_guide_src/source/testing/overview/013.php

@@ -1,7 +1,9 @@
 <?php
 
+use App\Libraries\Foo;
+
 // Create an instance of the class to test
-$obj = new \Foo();
+$obj = new Foo();
 
 // Get the invoker for the 'privateMethod' method.
 $method = $this->getPrivateMethodInvoker($obj, 'privateMethod');

user_guide_src/source/testing/overview/014.php

@@ -1,7 +1,9 @@
 <?php
 
+use App\Libraries\Foo;
+
 // Create an instance of the class to test
-$obj = new \Foo();
+$obj = new Foo();
 
 // Test the value
 $this->assertEquals('bar', $this->getPrivateProperty($obj, 'baz'));

user_guide_src/source/testing/overview/015.php

@@ -1,7 +1,9 @@
 <?php
 
+use App\Libraries\Foo;
+
 // Create an instance of the class to test
-$obj = new \Foo();
+$obj = new Foo();
 
 // Set the value
 $this->setPrivateProperty($obj, 'baz', 'oops!');