I downloaded the latest source code, built the plugin locally, restarted Xcode, clicked on view > Xcodecoverage > show code coverage to turn it on, ran the unit test.
in the OS X console, i get the following:
6/1/15 10:45:48.979 Xcode[95690]: COVLog Show coverage tapped.
6/1/15 10:45:48.980 Xcode[95690]: COVLog Doing an auto search.
6/1/15 10:45:49.180 Xcode[95690]: COVLog Looking in relative path
6/1/15 10:45:49.181 Xcode[95690]: COVLog generating coverageMap
But no coverage is displayed in Xcode
Xcode 6.3.2, MacOSX 10.10.3