Add mailers' preview

config/application.rb

@@ -77,6 +77,9 @@ module DomainNameRegistry
     config.action_mailer.perform_deliveries = true
     config.action_mailer.raise_delivery_errors = true
 
+    # Override "spec/mailers/previews" that RSpec sets
+    config.action_mailer.preview_path = "#{Rails.root}/test/mailers/previews"
+
     config.action_mailer.smtp_settings = {
       address:              ENV['smtp_address'],
       port:                 ENV['smtp_port'],

config/environments/staging-example.rb

@@ -1 +1,5 @@
 require_relative 'production'
+
+Rails.application.configure do
+  config.action_mailer.show_previews = true
+end

test/mailers/previews/domain_delete_mailer_preview.rb

@@ -0,0 +1,15 @@
+class DomainDeleteMailerPreview < ActionMailer::Preview
+  def self.define_forced_templates
+    DomainDeleteMailer.force_delete_templates.each do |template_name|
+      define_method "forced_#{template_name}".to_sym do
+        domain = Domain.first
+        DomainDeleteMailer.forced(domain: domain,
+                                  registrar: domain.registrar,
+                                  registrant: domain.registrant,
+                                  template_name: template_name)
+      end
+    end
+  end
+
+  define_forced_templates
+end

test/mailers/previews/domain_expire_mailer_preview.rb

@@ -0,0 +1,7 @@
+class DomainExpireMailerPreview < ActionMailer::Preview
+  def expired
+    domain = Domain.first
+    DomainExpireMailer.expired(domain: domain,
+                               registrar: domain.registrar)
+  end
+end