Add scheduled email feature for reminders

spec/mailers/previews/reminder_mailer_preview.rb

@@ -0,0 +1,7 @@
+# Preview all emails at http://localhost:3000/rails/mailers/reminder_mailer
+class ReminderMailerPreview < ActionMailer::Preview
+  # Preview this email at http://localhost:3000/rails/mailers/reminder_mailer/schedule_email
+  def schedule_email
+    ReminderMailer.schedule_email(FactoryBot.build(:reminder), 'to@example.com')
+  end
+end

spec/mailers/reminder_mailer_spec.rb

@@ -0,0 +1,29 @@
+require 'rails_helper'
+
+RSpec.describe ReminderMailer, type: :mailer do
+  describe 'Email delivery' do
+    let(:reminder) { build :reminder }
+    let(:mail) { ReminderMailer.schedule_email reminder, 'to@example.org' }
+
+    it 'renders the headers' do
+      expect(mail.subject).to eq 'Reminder'
+      expect(mail.to).to eq ['to@example.org']
+      expect(mail.from).to eq ['from@example.com']
+    end
+
+    it 'renders the body' do
+      expect(mail.body.encoded).to have_content reminder.title
+      expect(mail.body.encoded).to have_content reminder.body
+    end
+  end
+
+  describe 'Scheduled email' do
+    before { clear_enqueued_jobs }
+    let(:reminder) { create :reminder }
+
+    it 'queues the reminder' do
+      expect { ReminderMailer.schedule_email(reminder, 'to@example.org').deliver_later(wait_until: reminder.date) }.to have_enqueued_job.on_queue('mailers')
+      expect { ReminderMailer.schedule_email(reminder, 'to@example.org').deliver_later(wait_until: reminder.date) }.to have_enqueued_job.at(reminder.date)
+    end
+  end
+end