diff --git a/tests/MockServiceProviderTest.php b/tests/MockServiceProviderTest.php
new file mode 100644
index 0000000..a1ad39c
--- /dev/null
+++ b/tests/MockServiceProviderTest.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Yii\Testing\Tests;
+
+use PHPUnit\Framework\TestCase;
+use Yiisoft\Yii\Testing\MockServiceProvider;
+
+class MockServiceProviderTest extends TestCase
+{
+    public function testGetDefinitionsWillReturnDefinitionsSetInArray(): void
+    {
+        $mockServiceProvider = new MockServiceProvider();
+        $mockServiceProvider->setDefinition('example-id-001', ['class' => 'Example1\Class1\Position1']);
+        $mockServiceProvider->setDefinition('example-id-002', 'Example1\Class2\Position2');
+        $mockServiceProvider->setDefinition('example-id-003', 'Example3\Class3\Position3');
+
+        $this->assertEquals([
+            'example-id-001' => ['class' => 'Example1\Class1\Position1'],
+            'example-id-002' => 'Example1\Class2\Position2',
+            'example-id-003' => 'Example3\Class3\Position3',
+        ], $mockServiceProvider->getDefinitions());
+    }
+
+    public function testGetExtensionsWillReturnEmptyArray(): void
+    {
+        $this->assertEmpty((new MockServiceProvider())->getExtensions());
+    }
+}
diff --git a/tests/ResponseGrabberTest.php b/tests/ResponseGrabberTest.php
new file mode 100644
index 0000000..741b329
--- /dev/null
+++ b/tests/ResponseGrabberTest.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Yii\Testing\Tests;
+
+use Nyholm\Psr7\Response;
+use PHPUnit\Framework\TestCase;
+use RuntimeException;
+use Yiisoft\Yii\Testing\ResponseAccessor;
+use Yiisoft\Yii\Testing\ResponseGrabber;
+
+class ResponseGrabberTest extends TestCase
+{
+    public function testGetResponseWillReturnResponseAccessorSetResponse(): void
+    {
+        $response = new Response(200, body: '{"key": "value"}', reason: 'Ok with body', version: '1.1');
+
+        $responseGrabber = new ResponseGrabber();
+        $responseGrabber->setResponse($response);
+
+        $this->assertEquals(new ResponseAccessor($response), $responseGrabber->getResponse());
+    }
+
+    public function testGetResponseWillThrowExceptionIfSetResponseIsCalledWithNullParameter(): void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('Response is null');
+
+        $responseGrabber = new ResponseGrabber();
+        $responseGrabber->setResponse(null);
+        $responseGrabber->getResponse();
+    }
+
+    public function testGetResponseWillThrowExceptionIfResponseIsNotSet(): void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('Response is null');
+
+        (new ResponseGrabber())->getResponse();
+    }
+}