Spec EnterpriseFee tax_category association

Co-authored-by: David Cook <david@redcliffs.net>

spec/models/enterprise_fee_spec.rb

@@ -5,6 +5,7 @@ require 'spec_helper'
 describe EnterpriseFee do
   describe "associations" do
     it { is_expected.to belong_to(:enterprise).required }
+    it { is_expected.to belong_to(:tax_category).optional }
   end
 
   describe "validations" do