WARNING: From function: testing
         on line 2 of /sass/spec/directives/warn/functions_in_stack/input.scss, in `issues-warning'
         from line 7 of /sass/spec/directives/warn/functions_in_stack/input.scss, in `calls-function-that-warns'
         from line 11 of /sass/spec/directives/warn/functions_in_stack/input.scss
