add cmd test for kubectl auth can-i

hack/lib/test.sh

@@ -286,6 +286,18 @@ kube::test::if_has_not_string() {
   fi
 }
 
+kube::test::if_empty_string() {
+  local match=$1
+  if [ -n "$match" ]; then
+    echo "$match is not empty"
+    caller
+    return 1
+  else
+    echo "Successful"
+    return 0
+  fi
+}
+
 # Returns true if the required resource is part of supported resources.
 # Expects env vars:
 #   SUPPORTED_RESOURCES: Array of all resources supported by the apiserver. "*"