The Job- and TaskManagerStartupTest both contain a test that verifies that the JM/TM fails when giving a non-writable directory.
In case of the TM this directory is used for temporary files, see testIODirectoryNotWritable.
In case of the JM this directory is given to the blobService, see testJobManagerStartupFails.
To that end it is necessary to create a non-writable directory. To verify that this is at all possible we first rule out the Windows OS (for which File#setWritable has no effect), and check the return value of File#setWritable, which according to the documentation returns true if the file was in fact marked as non-writable.
When playing around with the BuddyWorks CI i noticed that these tests did neither fail nor succeed; we are able to create a non-writable directory (which i verified by checking the actual permissions), but the JM/TM still start up fine. As a result the tests just run indefinitely since this case wasn't considered.
I'm still investigating why they don't fail; my current assumption is that in this case files simply don't inherit the permissions of the parent directory.
This means that the checks that the tests make aren't adequate. Instead of verifying the permissions on the directory I propose verifying the actual failure condition: That we can't create new files in this directory.