Test files contain ClamAV-Test-Signature. You need unrar 3.0 to detect the test signature in test-failure.rar. Only clamscan is able to scan this file (clamd only depends on libclamav which has no support for the new RAR format). Please use clamscan --unrar, and it will automatically switch to the unrar utility after an internal (libclamav's) RAR module error.