Currently the cache test writes to a 'tmp' directory under itself. utf8 normalizer test downloads files from the internet to a different subdirectory under that test. In a locked-down environment, such as when the phpbb source tree is read-only, these writes fail and the system administrator is not necessarily able to set up symlinks without affecting versioned files.
Proposed fix is to designate one directory, test/tmp, for storing all files that the test suite writes to. This ticket covers reworking the cache test.