[Puppet Users] erb template test if value in array

In an .erb template, I want to test if a value is in an array (and if yes
do something).

I thought the way to do it might me something like:

<% if @testservers.include? @fqdn %>
environment = test
<% else %>
environment = production
<% end %>

However that blows up complaining that .include is an undefined function.

Our version of puppet is 2.6.16 on the client and 2.7.12 on the
puppetmaster.

Can anyone help?