fix: unit test

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

tests/php/Unit/Service/SignFileServiceTest.php

@@ -264,6 +264,8 @@ public function testSignWithFileNotFound():void {
 		$file = new \OCA\Libresign\Db\File();
 		$file->setUserId('username');
 
+		$this->root->method('getFirstNodeById')
+			->willThrowException(new NotFoundException('File not found'));
 		$this->root->method('getUserFolder')
 			->willReturn($this->root);