Test::Harness is already includet in the sles perl package itself. To avoid conflicts Test/Harness.pm will be installed to /usr/lib/perl5/5.10.0/x8664-linux-thread-multi/Test/Harness.pm This means there will be two versions of the module.
In the default @INC array /usr/lib/perl5/5.10.0/x8664-linux-thread-multi will be the first directory to be searched in and perl will therefore load the Test::Harness module from this package.
This may or may not work for you. Consider updating perl instead of using this.