Spec helpers for asserting delivered emails

spec/controllers/workshop_invitation_controller_spec.rb

@@ -8,13 +8,6 @@
 
   before { login(member) }
 
-  # The invitation mailer sends multipart/mixed > multipart/alternative > text/html;
-  # the root body is empty, so read the nested html part.
-  def html_body(mail)
-    parts = mail.parts.flat_map { |part| part.multipart? ? part.parts : [part] }
-    parts.find { |part| part.content_type.match?('text/html') }&.body&.decoded
-  end
-
   describe 'GET #show' do
     it 'returns http success' do
       get :show, params: { id: invitation.token }
@@ -192,16 +185,16 @@ def html_body(mail)
       it 'emails the promoted member a confirmation they are attending' do
         post :reject, params: { id: invitation.token }
 
-        mail = ActionMailer::Base.deliveries.find { |m| m.to.include?(waitlisted_member.email) }
+        mail = delivered_emails_to(waitlisted_member).last
         expect(mail).not_to be_nil
-        expect(html_body(mail)).to include('been confirmed')
+        expect(email_html(mail)).to include('been confirmed')
       end
 
       it 'sends the promotion variant of the email (waiting-list flag set)' do
         post :reject, params: { id: invitation.token }
 
-        mail = ActionMailer::Base.deliveries.find { |m| m.to.include?(waitlisted_member.email) }
-        expect(html_body(mail)).to include('A spot became available and your attendance has now been confirmed!')
+        expect(email_html(delivered_emails_to(waitlisted_member).last))
+          .to include('A spot became available and your attendance has now been confirmed!')
       end
 
       it 'does not email anyone else (the rejecting member gets no promotion copy)' do

spec/shared_contexts/email_helpers_spec.rb

@@ -0,0 +1,25 @@
+require 'rails_helper'
+
+# Canary for EmailHelpers — same pattern as the 'with forgery protection
+# enforced' canary. It delivers a real invitation email so a change to the
+# mailer's part structure or to the test delivery path fails here instead of
+# silently weakening every email assertion that uses the helper.
+RSpec.describe EmailHelpers do
+  let(:member) { Fabricate(:member) }
+  let(:workshop) { Fabricate(:workshop) }
+  let(:invitation) { Fabricate(:workshop_invitation, workshop:, member:) }
+
+  it 'delivered_emails_to filters delivered mail by recipient' do
+    WorkshopInvitationMailer.attending(workshop, member, invitation, false).deliver_now
+
+    expect(delivered_emails_to(member)).not_to be_empty
+    expect(delivered_emails_to('nobody@example.com')).to be_empty
+  end
+
+  it 'email_html reads the waiting-list html copy from the nested part' do
+    WorkshopInvitationMailer.attending(workshop, member, invitation, true).deliver_now
+
+    expect(email_html(delivered_emails_to(member).last))
+      .to include('A spot became available and your attendance has now been confirmed!')
+  end
+end

spec/spec_helper.rb

@@ -50,6 +50,7 @@
 RSpec.configure do |config|
   config.include ActiveJob::TestHelper
   config.include ApplicationHelper
+  config.include EmailHelpers
   config.include LoginHelpers
   config.include ActiveSupport::Testing::TimeHelpers
   config.include SelectFromChosen, type: :feature

spec/support/helpers/email_helpers.rb

@@ -0,0 +1,18 @@
+module EmailHelpers
+  # Mails the test-delivery path collected for a recipient (a Member or an
+  # address). The test queue adapter is delayed_job with Delayed::Worker.delay_jobs
+  # set to false in test, so deliver_later delivers immediately and mail lands in
+  # ActionMailer::Base.deliveries.
+  def delivered_emails_to(recipient)
+    address = recipient.respond_to?(:email) ? recipient.email : recipient
+    ActionMailer::Base.deliveries.select { |mail| mail.to.include?(address) }
+  end
+
+  # Decoded text/html body of a delivered Mail::Message. The invitation mailers
+  # send multipart/mixed > multipart/alternative > text/html, so the root
+  # mail.body.decoded is empty and the html part must be read directly.
+  def email_html(mail)
+    parts = mail.parts.flat_map { |part| part.multipart? ? part.parts : [part] }
+    parts.find { |part| part.content_type.match?('text/html') }&.body&.decoded
+  end
+end