Rewrite `clustering` example test to avoid false failures
Rewrite `clustering` example test to avoid false failures

LogtalkDotOrg/logtalk3,LogtalkDotOrg/logtalk3,LogtalkDotOrg/logtalk3,LogtalkDotOrg/logtalk3,LogtalkDotOrg/logtalk3,LogtalkDotOrg/logtalk3,LogtalkDotOrg/logtalk3