Testbase: Folder creation with 0777 permissions.
During the creation of the test environment for the Acceptance Tests via Codeception,
\TYPO3\CMS\Core\Tests\Testbase->createDirectory($directory) creates folders with 0777 permission. However because of the umask value it is not possible to set permissions of the newly created folder to 0777.
As of right now only the owner of the folder is able to write (at least on my local Ubuntu 18.04 machine).
It is possible to set the umask value temporarily to 0, that makes it possible to set 0777:
$oldmask = umask(0); mkdir("test", 0777); umask($oldmask);