app/views/test_messages/new.html.erb
<%= render 'header', :title => 'Send test message' %>
<section class="main-content">
<%= render "flashes" -%>
<%= simple_form_for :test_message, url: @url do |form| %>
<%= form.input :body, input_html: { value: @message.body }, readonly: true, label: "Message body to send (to edit, update the scheduled message you are testing)" %>
<%= form.input :slack_username, label: "Slack username to send test to", as: :string %>
<%= form.submit "Send test" %>
<% end %>
</section>