The "fail the build if no test results are present" option doesn't fail the job. The tap results file exists and contains a single string (not test results).
TAP Reports Processing: START
Looking for TAP results report in workspace using pattern: js_unittest_results.txt
Parsing TAP test result [/var/lib/jenkins/jobs/testing/builds/2014-03-18_13-04-29/tap-master-files/js_unittest_results.txt].
TAP Reports Processing: FINISH
[bmannix@glados ~]$ cat /var/lib/jenkins/jobs/testing/builds/2014-03-18_13-04-29/tap-master-files/js_unittest_results.txt
The build fails based on not finding any tap test results.