refactor(tests): convert subscription email feature tests to delivery assertions

Replaces expect_any_instance_of mocks with ActionMailer::Base.deliveries
verification for all welcome email scenarios.

Changes:
- First-time coach subscription - verifies email sent and contains 'coach'
- First-time student subscription - verifies email sent and contains 'student'
- Second subscription tests - clears deliveries and verifies no new emails
- Unsubscribe/resubscribe tests - verifies no duplicate emails sent

Adds before hook to clear deliveries for consistent test isolation.

Removes all expect_any_instance_of(MemberMailer) mocks which were
problematic for parallel test execution.

Author: mroderick

spec/features/subscribing_to_emails_spec.rb

@@ -24,62 +24,76 @@
   end
 
   context 'a member receives a welcome email' do
+    before do
+      ActionMailer::Base.deliveries.clear
+    end
+
     scenario 'Subscribing to a coach mailing list for the first time sends a coach email to the user' do
       coach_group = Fabricate(:coaches)
-      expect_any_instance_of(MemberMailer).to receive(:welcome_coach)
-      expect_any_instance_of(MemberMailer).not_to receive(:welcome_students)
 
       visit subscriptions_path
       click_on "#{coach_group.chapter.name}-coaches"
+
+      welcome_emails = ActionMailer::Base.deliveries.select { |e| e.to.include?(member.email) }
+      expect(welcome_emails.count).to eq(1)
+      expect(welcome_emails.first.body.encoded).to include('coach')
     end
 
     scenario 'Subscribing to a student mailing list for the first time sends a student email to the user' do
-      expect_any_instance_of(MemberMailer).to receive(:welcome_student)
-      expect_any_instance_of(MemberMailer).not_to receive(:welcome_coach)
-
       visit subscriptions_path
       click_on "#{group.chapter.name}-students"
+
+      welcome_emails = ActionMailer::Base.deliveries.select { |e| e.to.include?(member.email) }
+      expect(welcome_emails.count).to eq(1)
+      expect(welcome_emails.first.body.encoded).to include('student')
     end
 
     scenario "Subscribing to a second coach mailing list doesn't send another mail" do
       coach_groups = Fabricate.times(2, :coaches)
-      expect_any_instance_of(MemberMailer).to receive(:welcome_coach).once
-      expect_any_instance_of(MemberMailer).not_to receive(:welcome_students)
 
       visit subscriptions_path
       click_on "#{coach_groups[0].chapter.name}-coaches"
+      ActionMailer::Base.deliveries.clear
       click_on "#{coach_groups[1].chapter.name}-coaches"
+
+      welcome_emails = ActionMailer::Base.deliveries.select { |e| e.to.include?(member.email) }
+      expect(welcome_emails.count).to eq(0)
     end
 
     scenario "Subscribing to a second student mailing list doesn't send another mail" do
-      expect_any_instance_of(MemberMailer).to receive(:welcome_student).once
-      expect_any_instance_of(MemberMailer).not_to receive(:welcome_coach)
       extra_student_group = Fabricate(:students)
 
       visit subscriptions_path
       click_on "#{group.chapter.name}-students"
+      ActionMailer::Base.deliveries.clear
       click_on "#{extra_student_group.chapter.name}-students"
+
+      welcome_emails = ActionMailer::Base.deliveries.select { |e| e.to.include?(member.email) }
+      expect(welcome_emails.count).to eq(0)
     end
 
     scenario "Unsubscribing and re-subscribing doesn't send a second mail to a coach" do
       coach_group = Fabricate(:coaches)
-      expect_any_instance_of(MemberMailer).to receive(:welcome_coach).once
-      expect_any_instance_of(MemberMailer).not_to receive(:welcome_students)
 
       visit subscriptions_path
       click_on "#{coach_group.chapter.name}-coaches"
+      ActionMailer::Base.deliveries.clear
       click_on "#{coach_group.chapter.name}-coaches"
       click_on "#{coach_group.chapter.name}-coaches"
+
+      welcome_emails = ActionMailer::Base.deliveries.select { |e| e.to.include?(member.email) }
+      expect(welcome_emails.count).to eq(0)
     end
 
     scenario "Unsubscribing and re-subscribing doesn't send a second mail to a student" do
-      expect_any_instance_of(MemberMailer).to receive(:welcome_student).once
-      expect_any_instance_of(MemberMailer).not_to receive(:welcome_coach)
-
       visit subscriptions_path
       click_on "#{group.chapter.name}-students"
+      ActionMailer::Base.deliveries.clear
       click_on "#{group.chapter.name}-students"
       click_on "#{group.chapter.name}-students"
+
+      welcome_emails = ActionMailer::Base.deliveries.select { |e| e.to.include?(member.email) }
+      expect(welcome_emails.count).to eq(0)
     end
   end
 end