How to use Concat Operator in Smarty?

How to use concat operator

{$obj->calledFunc('string const')|cat:$var}

In my case I wanted to use in a project of SKADATE

{ assign var='test1' value="custom.event_activity"}                     
{ assign var='test2' value=$event.dto->getActivity()}                     
{ assign var='var' value="." }
{ assign var='test3' value=$test1|cat:$var}                     
{ assign var='test4' value=$test3|cat:$test2} 

{text %.$test4}