diff --git a/tests/ApiTest.php b/tests/ApiTest.php
index 4e4e1f7..7caaefa 100644
--- a/tests/ApiTest.php
+++ b/tests/ApiTest.php
@@ -2051,4 +2051,82 @@ final class ApiTest extends TestCase
             unlink($filePath);
         }
     }
+
+    #[Test]
+    public function uploadFileUsesMultipartForSmallFiles(): void
+    {
+        $uploadUrl = 'https://upload.server/path';
+        $fileName = 'small.txt';
+        $fileContents = 'content';
+        $fileHandle = fopen('php://memory', 'w+');
+        fwrite($fileHandle, $fileContents);
+        rewind($fileHandle);
+
+        $smallFileSize = strlen($fileContents);
+        $expectedResponse = 'multipart-response';
+
+        $fstatMock = $this->getFunctionMock('BushlanovDev\MaxMessengerBot', 'fstat');
+        $fstatMock->expects($this->once())->with($fileHandle)->willReturn(['size' => $smallFileSize]);
+
+        $this->clientMock
+            ->expects($this->once())
+            ->method('multipartUpload')
+            ->with($uploadUrl, $fileHandle, $fileName)
+            ->willReturn($expectedResponse);
+
+        $this->clientMock
+            ->expects($this->never())
+            ->method('resumableUpload');
+
+        $result = $this->api->uploadFile($uploadUrl, $fileHandle, $fileName);
+
+        $this->assertSame($expectedResponse, $result);
+        fclose($fileHandle);
+    }
+
+    #[Test]
+    public function uploadFileUsesResumableForLargeFiles(): void
+    {
+        $uploadUrl = 'https://upload.server/path';
+        $fileName = 'large.zip';
+        $fileHandle = fopen('php://memory', 'w+');
+
+        rewind($fileHandle);
+
+        $largeFileSize = 10 * 1024 * 1024;
+        $expectedResponse = 'resumable-response';
+
+        $fstatMock = $this->getFunctionMock('BushlanovDev\MaxMessengerBot', 'fstat');
+        $fstatMock->expects($this->once())->with($fileHandle)->willReturn(['size' => $largeFileSize]);
+
+        $this->clientMock
+            ->expects($this->once())
+            ->method('resumableUpload')
+            ->with($uploadUrl, $fileHandle, $fileName, $largeFileSize)
+            ->willReturn($expectedResponse);
+
+        $this->clientMock
+            ->expects($this->never())
+            ->method('multipartUpload');
+
+        $result = $this->api->uploadFile($uploadUrl, $fileHandle, $fileName);
+
+        $this->assertSame($expectedResponse, $result);
+        fclose($fileHandle);
+    }
+
+    #[Test]
+    public function uploadFileThrowsExceptionWhenFstatFails(): void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('File handle is not a valid resource.');
+
+        $fileHandle = fopen('php://memory', 'r');
+
+        $fstatMock = $this->getFunctionMock('BushlanovDev\MaxMessengerBot', 'fstat');
+        $fstatMock->expects($this->once())->with($fileHandle)->willReturn(false);
+
+        $this->api->uploadFile('http://a.b', $fileHandle, 'file.txt');
+        fclose($fileHandle);
+    }
 }
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
index 4c2156f..00b901d 100644
--- a/tests/ClientTest.php
+++ b/tests/ClientTest.php
@@ -332,7 +332,7 @@ final class ClientTest extends TestCase
         $this->requestFactoryMock->method('createRequest')->willReturn($this->requestMock);
         $this->requestMock->method('withHeader')->willReturn($this->requestMock);
         $this->requestMock->method('withBody')->willReturn($this->requestMock);
-        $this->httpClientMock->method('sendRequest')->willReturn($this->responseMock);
+//        $this->httpClientMock->method('sendRequest')->willReturn($this->responseMock);
         $this->responseMock->method('getStatusCode')->willReturn(200);
         $this->streamMock->method('__toString')->willReturn(json_encode($responsePayload));
 
@@ -409,4 +409,46 @@ final class ClientTest extends TestCase
         $result = $this->client->multipartUpload($uploadUrl, $fileContents, $fileName);
         $this->assertSame($rawResponse, $result);
     }
+
+    #[Test]
+    public function resumableUploadThrowsExceptionForInvalidResource(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('fileResource must be a valid stream resource.');
+
+        $this->client->resumableUpload('http://a.b', 'not-a-resource', 'file.txt', 100);
+    }
+
+    #[Test]
+    public function resumableUploadThrowsExceptionForZeroFileSize(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('File size must be greater than 0.');
+
+        $fileResource = fopen('php://memory', 'r');
+        $this->client->resumableUpload('http://a.b', $fileResource, 'file.txt', 0);
+        fclose($fileResource);
+    }
+
+    #[Test]
+    public function resumableUploadThrowsNetworkExceptionOnChunkUploadFailure(): void
+    {
+        $this->expectException(NetworkException::class);
+
+        $fileResource = fopen('php://memory', 'w+');
+        fwrite($fileResource, 'some data');
+        rewind($fileResource);
+
+        $this->requestFactoryMock->method('createRequest')->willReturn($this->requestMock);
+        $this->requestMock->method('withBody')->willReturnSelf();
+        $this->requestMock->method('withHeader')->willReturnSelf();
+
+        $psrException = new class extends \Exception implements ClientExceptionInterface {};
+        $this->httpClientMock
+            ->method('sendRequest')
+            ->willThrowException($psrException);
+
+        $this->client->resumableUpload('http://a.b', $fileResource, 'file.txt', 9);
+        fclose($fileResource);
+    }
 }