add unit test for GetUniqueStrings
add unit test for GetUniqueStrings

Signed-off-by: Zhou Hao <f577ade201aa03d612c19915a089dc6084d45cd9@cn.fujitsu.com>

robinpercy/kops,kubernetes/kops,robinpercy/kops,justinsb/kops,robinpercy/kops,robinpercy/kops,kubernetes/kops,justinsb/kops,justinsb/kops,kubernetes/kops