diff --git a/app/code/Magento/Captcha/Test/Unit/Observer/CheckGuestCheckoutObserverTest.php b/app/code/Magento/Captcha/Test/Unit/Observer/CheckGuestCheckoutObserverTest.php
new file mode 100644
index 0000000000000..d3f29fae8a592
--- /dev/null
+++ b/app/code/Magento/Captcha/Test/Unit/Observer/CheckGuestCheckoutObserverTest.php
@@ -0,0 +1,211 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Captcha\Test\Unit\Observer;
+
+use Magento\Captcha\Model\DefaultModel as CaptchaModel;
+use Magento\Captcha\Observer\CheckGuestCheckoutObserver;
+use Magento\Captcha\Helper\Data as CaptchaDataHelper;
+use Magento\Framework\App\Action\Action;
+use Magento\Framework\App\ActionFlag;
+use Magento\Captcha\Observer\CaptchaStringResolver;
+use Magento\Checkout\Model\Type\Onepage;
+use Magento\Framework\App\Request\Http;
+use Magento\Framework\App\Response\Http as HttpResponse;
+use Magento\Framework\Event\Observer;
+use Magento\Framework\Json\Helper\Data as JsonHelper;
+use Magento\Framework\TestFramework\Unit\Helper\ObjectManager;
+use Magento\Quote\Model\Quote;
+
+/**
+ * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
+ */
+class CheckGuestCheckoutObserverTest extends \PHPUnit\Framework\TestCase
+{
+    const FORM_ID = 'guest_checkout';
+
+    /**
+     * @var CheckGuestCheckoutObserver
+     */
+    private $checkGuestCheckoutObserver;
+
+    /**
+     * @var ObjectManager
+     */
+    private $objectManager;
+
+    /**
+     * @var Observer
+     */
+    private $observer;
+
+    /**
+     * @var HttpResponse|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $responseMock;
+
+    /**
+     * @var HttpResponse|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $requestMock;
+
+    /**
+     * @var ActionFlag|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $actionFlagMock;
+
+    /**
+     * @var CaptchaStringResolver|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $captchaStringResolverMock;
+
+    /**
+     * @var JsonHelper|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $jsonHelperMock;
+
+    /**
+     * @var CaptchaModel|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $captchaModelMock;
+
+    /**
+     * @var  Quote|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $quoteModelMock;
+
+    /**
+     * @var Action|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $controllerMock;
+
+    protected function setUp()
+    {
+        $onepageModelTypeMock = $this->createMock(Onepage::class);
+        $captchaHelperMock = $this->createMock(CaptchaDataHelper::class);
+        $this->objectManager = new ObjectManager($this);
+        $this->actionFlagMock = $this->createMock(ActionFlag::class);
+        $this->captchaStringResolverMock = $this->createMock(CaptchaStringResolver::class);
+        $this->captchaModelMock = $this->createMock(CaptchaModel::class);
+        $this->quoteModelMock = $this->createMock(Quote::class);
+        $this->controllerMock = $this->createMock(Action::class);
+        $this->requestMock = $this->createMock(Http::class);
+        $this->responseMock = $this->createMock(HttpResponse::class);
+        $this->observer = new Observer(['controller_action' => $this->controllerMock]);
+        $this->jsonHelperMock = $this->createMock(JsonHelper::class);
+
+        $this->checkGuestCheckoutObserver = $this->objectManager->getObject(
+            CheckGuestCheckoutObserver::class,
+            [
+                'helper' => $captchaHelperMock,
+                'actionFlag' => $this->actionFlagMock,
+                'captchaStringResolver' => $this->captchaStringResolverMock,
+                'typeOnepage' => $onepageModelTypeMock,
+                'jsonHelper' => $this->jsonHelperMock
+            ]
+        );
+
+        $captchaHelperMock->expects($this->once())
+            ->method('getCaptcha')
+            ->with(self::FORM_ID)
+            ->willReturn($this->captchaModelMock);
+        $onepageModelTypeMock->expects($this->once())
+            ->method('getQuote')
+            ->willReturn($this->quoteModelMock);
+    }
+
+    public function testCheckGuestCheckoutForRegister()
+    {
+        $this->quoteModelMock->expects($this->once())
+            ->method('getCheckoutMethod')
+            ->willReturn(Onepage::METHOD_REGISTER);
+        $this->captchaModelMock->expects($this->never())
+            ->method('isRequired');
+
+        $this->checkGuestCheckoutObserver->execute($this->observer);
+    }
+
+    public function testCheckGuestCheckoutWithNoCaptchaRequired()
+    {
+        $this->quoteModelMock->expects($this->once())
+            ->method('getCheckoutMethod')
+            ->willReturn(Onepage::METHOD_GUEST);
+        $this->captchaModelMock->expects($this->once())
+            ->method('isRequired')
+            ->willReturn(false);
+        $this->captchaModelMock->expects($this->never())
+            ->method('isCorrect');
+
+        $this->checkGuestCheckoutObserver->execute($this->observer);
+    }
+
+    public function testCheckGuestCheckoutWithIncorrectCaptcha()
+    {
+        $captchaValue = 'some_word';
+        $encodedJsonValue = '{}';
+
+        $this->quoteModelMock->expects($this->once())
+            ->method('getCheckoutMethod')
+            ->willReturn(Onepage::METHOD_GUEST);
+        $this->captchaModelMock->expects($this->once())
+            ->method('isRequired')
+            ->willReturn(true);
+        $this->controllerMock->expects($this->once())
+            ->method('getRequest')
+            ->willReturn($this->requestMock);
+        $this->controllerMock->expects($this->once())
+            ->method('getResponse')
+            ->willReturn($this->responseMock);
+        $this->controllerMock->expects($this->once())
+            ->method('getResponse')
+            ->willReturn($this->responseMock);
+        $this->captchaStringResolverMock->expects($this->once())
+            ->method('resolve')
+            ->with($this->requestMock, self::FORM_ID)
+            ->willReturn($captchaValue);
+        $this->captchaModelMock->expects($this->once())
+            ->method('isCorrect')
+            ->with($captchaValue)
+            ->willReturn(false);
+        $this->actionFlagMock->expects($this->once())
+            ->method('set')
+            ->with('', Action::FLAG_NO_DISPATCH, true);
+        $this->jsonHelperMock->expects($this->once())
+            ->method('jsonEncode')
+            ->willReturn($encodedJsonValue);
+        $this->responseMock->expects($this->once())
+            ->method('representJson')
+            ->with($encodedJsonValue);
+
+        $this->checkGuestCheckoutObserver->execute($this->observer);
+    }
+
+    public function testCheckGuestCheckoutWithCorrectCaptcha()
+    {
+        $this->quoteModelMock->expects($this->once())
+            ->method('getCheckoutMethod')
+            ->willReturn(Onepage::METHOD_GUEST);
+        $this->captchaModelMock->expects($this->once())
+            ->method('isRequired')
+            ->willReturn(true);
+        $this->controllerMock->expects($this->once())
+            ->method('getRequest')
+            ->willReturn($this->requestMock);
+        $this->captchaStringResolverMock->expects($this->once())
+            ->method('resolve')
+            ->with($this->requestMock, self::FORM_ID)
+            ->willReturn('some_word');
+        $this->captchaModelMock->expects($this->once())
+            ->method('isCorrect')
+            ->with('some_word')
+            ->willReturn(true);
+        $this->actionFlagMock->expects($this->never())
+            ->method('set');
+
+        $this->checkGuestCheckoutObserver->execute($this->observer);
+    }
+}