Add minimal test for existing followup search feature

app/models/channel/email_parser.rb

@@ -134,7 +134,7 @@ returns
     UserInfo.current_user_id = 1
     filters = {}
     Setting.where(area: 'Postmaster::PreFilter').order(:name).each do |setting|
-      filters[setting.name] = Kernel.const_get(Setting.get(setting.name))
+      filters[setting.name] = Setting.get(setting.name).constantize
     end
     filters.each do |key, backend|
       Rails.logger.debug { "run postmaster pre filter #{key}: #{backend}" }

spec/models/channel/email_parser_spec.rb

@@ -0,0 +1,34 @@
+require 'rails_helper'
+
+RSpec.describe Channel::EmailParser, type: :model do
+  let(:ticket) { create(:ticket) }
+  let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail001.box') }
+  let(:raw_mail) { File.read(mail_file).sub(/(?<=^Subject: ).*$/, test_string) }
+  let(:test_string) do
+    Setting.get('ticket_hook') + Setting.get('ticket_hook_divider') + ticket.number
+  end
+
+  describe '#process' do
+    context 'when email subject contains ticket reference' do
+      it 'adds message to ticket' do
+        expect { described_class.new.process({}, raw_mail) }
+          .to change { ticket.articles.length }
+      end
+    end
+
+    context 'when configured to search body' do
+      before { Setting.set('postmaster_follow_up_search_in', 'body') }
+
+      context 'when body contains ticket reference' do
+        context 'in visible text' do
+          let(:raw_mail) { File.read(mail_file).sub(/Hallo =\nMartin,(?=<o:p>)/, test_string) }
+
+          it 'adds message to ticket' do
+            expect { described_class.new.process({}, raw_mail) }
+              .to change { ticket.articles.length }
+          end
+        end
+      end
+    end
+  end
+end