Concatenate field and String

First Sry for my bad englisch
I am using logstash since 2 days
I want to concatenate a field and a String in the field

Like the field is "Test" and i want to add a "_NR1" to the end

Thanks for help

Problem solved

add_field => {
zusatz => "NR_2"
gesammt => "%{Test_var} %{zusatz}"