diff --git a/app/code/Magento/Captcha/Test/Unit/Observer/CaptchaStringResolverTest.php b/app/code/Magento/Captcha/Test/Unit/Observer/CaptchaStringResolverTest.php
new file mode 100644
index 0000000000000..2bd8ac6f16986
--- /dev/null
+++ b/app/code/Magento/Captcha/Test/Unit/Observer/CaptchaStringResolverTest.php
@@ -0,0 +1,69 @@
+<?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\Helper\Data as CaptchaDataHelper;
+use Magento\Captcha\Observer\CaptchaStringResolver;
+use Magento\Framework\App\Request\Http as HttpRequest;
+use Magento\Framework\TestFramework\Unit\Helper\ObjectManager;
+
+class CaptchaStringResolverTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @var ObjectManager
+     */
+    private $objectManagerHelper;
+
+    /**
+     * @var CaptchaStringResolver
+     */
+    private $captchaStringResolver;
+
+    /**
+     * @var HttpRequest|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $requestMock;
+
+    protected function setUp()
+    {
+        $this->objectManagerHelper = new ObjectManager($this);
+        $this->requestMock = $this->createMock(HttpRequest::class);
+        $this->captchaStringResolver = $this->objectManagerHelper->getObject(CaptchaStringResolver::class);
+    }
+
+    public function testResolveWithFormIdSet()
+    {
+        $formId = 'contact_us';
+        $captchaValue = 'some-value';
+
+        $this->requestMock->expects($this->once())
+            ->method('getPost')
+            ->with(CaptchaDataHelper::INPUT_NAME_FIELD_VALUE)
+            ->willReturn([$formId => $captchaValue]);
+
+        self::assertEquals(
+            $this->captchaStringResolver->resolve($this->requestMock, $formId),
+            $captchaValue
+        );
+    }
+
+    public function testResolveWithNoFormIdInRequest()
+    {
+        $formId = 'contact_us';
+
+        $this->requestMock->expects($this->once())
+            ->method('getPost')
+            ->with(CaptchaDataHelper::INPUT_NAME_FIELD_VALUE)
+            ->willReturn([]);
+
+        self::assertEquals(
+            $this->captchaStringResolver->resolve($this->requestMock, $formId),
+            ''
+        );
+    }
+}