Improve domain discard

- Extract rake task domain:discard
- Remove background job when keeping a domain

#790

test/integration/tasks/discard_domain_test.rb

@@ -0,0 +1,43 @@
+require 'test_helper'
+
+class DiscardDomainTaskTest < ActiveSupport::TestCase
+  setup do
+    travel_to Time.zone.parse('2010-07-05 08:00')
+    @domain = domains(:shop)
+  end
+
+  def test_discard_domains_with_past_delete_at
+    @domain.update!(delete_at: Time.zone.parse('2010-07-05 07:59'))
+    Rake::Task['domain:discard'].execute
+    @domain.reload
+    assert @domain.discarded?
+  end
+
+  def test_ignore_domains_with_delete_at_in_the_future_or_now
+    @domain.update!(delete_at: Time.zone.parse('2010-07-05 08:00'))
+    Rake::Task['domain:discard'].execute
+    @domain.reload
+    refute @domain.discarded?
+  end
+
+  def test_ignore_already_discarded_domains
+    @domain.update!(delete_at: Time.zone.parse('2010-07-05 07:59'))
+    @domain.discard
+
+    job_count = lambda do
+      QueJob.where("args->>0 = '#{@domain.id}'", job_class: DomainDeleteJob.name).count
+    end
+
+    assert_no_difference job_count, 'A domain should not be discarded again' do
+      Rake::Task['domain:discard'].execute
+    end
+  end
+
+  def test_ignore_domains_with_server_delete_prohibited_status
+    @domain.update!(delete_at: Time.zone.parse('2010-07-05 07:59'),
+                    statuses: [DomainStatus::SERVER_DELETE_PROHIBITED])
+    Rake::Task['domain:discard'].execute
+    @domain.reload
+    refute @domain.discarded?
+  end
+end