diff --git a/tests/Behat/Context/System/FilesystemContext.php b/tests/Behat/Context/System/FilesystemContext.php
index ab2372b9..6c4d9bf4 100644
--- a/tests/Behat/Context/System/FilesystemContext.php
+++ b/tests/Behat/Context/System/FilesystemContext.php
@@ -30,6 +30,7 @@ public function before(): void
      */
     public function thereIsAFileWithNameAndContent(string $filename, string $date): void
     {
+        Assert::notNull($this->vfsStream);
         vfsStream::newFile($filename)->at($this->vfsStream)->setContent($date);
     }