docs: update sample code style

Author: kenjis

user_guide_src/source/testing/overview/016.php

@@ -1,14 +1,17 @@
 <?php
 
+namespace Tests;
+
+use CodeIgniter\HTTP\CURLRequest;
 use CodeIgniter\Test\CIUnitTestCase;
 use Config\Services;
 
 final class SomeTest extends CIUnitTestCase
 {
     public function testSomething()
     {
-        $curlrequest = $this->getMockBuilder('CodeIgniter\HTTP\CURLRequest')
-            ->setMethods(['request'])
+        $curlrequest = $this->getMockBuilder(CURLRequest::class)
+            ->onlyMethods(['request'])
             ->getMock();
         Services::injectMock('curlrequest', $curlrequest);
 

user_guide_src/source/testing/overview/017.php

@@ -2,6 +2,7 @@
 
 namespace Tests;
 
+use App\Models\UserModel;
 use CodeIgniter\Config\Factories;
 use CodeIgniter\Test\CIUnitTestCase;
 use Tests\Support\Mock\MockUserModel;
@@ -13,6 +14,6 @@ protected function setUp(): void
         parent::setUp();
 
         $model = new MockUserModel();
-        Factories::injectMock('models', 'App\Models\UserModel', $model);
+        Factories::injectMock('models', UserModel::class, $model);
     }
 }