Fix failing Unit Test and refactor main class

Author: lbajsarowicz

app/code/Magento/Captcha/Controller/Refresh/Index.php

@@ -3,6 +3,8 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+declare(strict_types=1);
+
 namespace Magento\Captcha\Controller\Refresh;
 
 use Magento\Captcha\Helper\Data as CaptchaHelper;
@@ -68,6 +70,26 @@ public function __construct(
      * @inheritdoc
      */
     public function execute()
+    {
+        $formId = $this->getRequestFormId();
+
+        $captchaModel = $this->captchaHelper->getCaptcha($formId);
+        $captchaModel->generate();
+
+        $block = $this->layout->createBlock($captchaModel->getBlockName());
+        $block->setFormId($formId)->setIsAjax(true)->toHtml();
+
+        $result = $this->jsonResultFactory->create();
+
+        return $result->setData(['imgSrc' => $captchaModel->getImgSrc()]);
+    }
+
+    /**
+     * Returns requested Form ID
+     *
+     * @return string|null
+     */
+    private function getRequestFormId(): ?string
     {
         $formId = $this->request->getPost('formId');
         if (null === $formId) {
@@ -76,15 +98,10 @@ public function execute()
             if ($content) {
                 $params = $this->serializer->unserialize($content);
             }
-            $formId = isset($params['formId']) ? $params['formId'] : null;
-        }
-        $captchaModel = $this->captchaHelper->getCaptcha($formId);
-        $captchaModel->generate();
 
-        $block = $this->layout->createBlock($captchaModel->getBlockName());
-        $block->setFormId($formId)->setIsAjax(true)->toHtml();
+            $formId = $params['formId'] ?? null;
+        }
 
-        $result = $this->jsonResultFactory->create();
-        return $result->setData(['imgSrc' => $captchaModel->getImgSrc()]);
+        return $formId !== null ? (string)$formId : null;
     }
 }

app/code/Magento/Captcha/Test/Unit/Controller/Refresh/IndexTest.php

@@ -9,6 +9,7 @@
 use Magento\Captcha\Helper\Data as CaptchaHelper;
 use Magento\Captcha\Model\CaptchaInterface;
 use Magento\Framework\App\RequestInterface;
+use Magento\Framework\Controller\Result\Json as ResultJson;
 use Magento\Framework\Controller\Result\JsonFactory as ResultJsonFactory;
 use Magento\Framework\Serialize\Serializer\Json as JsonSerializer;
 use Magento\Framework\View\Element\BlockInterface;
@@ -27,6 +28,9 @@ class IndexTest extends TestCase
     /** @var MockObject|ResultJsonFactory */
     private $jsonResultFactoryMock;
 
+    /** @var MockObject|ResultJson */
+    private $jsonResultMock;
+
     /** @var MockObject|CaptchaHelper */
     private $captchaHelperMock;
 
@@ -54,6 +58,9 @@ protected function setUp()
             ->setMethods(['setFormId', 'setIsAjax', 'toHtml'])
             ->getMockForAbstractClass();
         $this->jsonResultFactoryMock = $this->createMock(ResultJsonFactory::class);
+        $this->jsonResultMock = $this->createMock(ResultJson::class);
+        $this->jsonResultFactoryMock->method('create')
+            ->willReturn($this->jsonResultMock);
         $this->jsonSerializerMock = $this->createMock(JsonSerializer::class);
         $this->captchaHelperMock = $this->createMock(CaptchaHelper::class);