Adds tests for the StagingInterceptor to boost coverage

spec/mailers/staging_interceptor_spec.rb

@@ -0,0 +1,24 @@
+require 'rails_helper'
+
+RSpec.describe Interceptors::StagingInterceptor, type: :mailer do
+  around do |test|
+    ActionMailer::Base.register_interceptor(Interceptors::StagingInterceptor)
+    test.run
+    ActionMailer::Base.unregister_interceptor(Interceptors::StagingInterceptor)
+  end
+
+  it 'rewrites outbound mail to the test list' do
+    mail = NotificationsMailer.#
+    mail.cc %w[a@berkeley.edu b@berkeley.edu]
+    mail.bcc %w[c@berkeley.edu d@berkeley.edu]
+    mail.deliver_now
+
+    expect(mail.to).to eq %w[lib-testmail@lists.berkeley.edu]
+    expect(mail.cc).to be_empty
+    expect(mail.bcc).to be_empty
+    expect(mail.header[:x_lap_service].value).to eq 'geodata'
+    expect(mail.header[:x_original_to].value).to eq 'fake@berkeley.edu'
+    expect(mail.header[:x_original_cc].value).to eq 'a@berkeley.edu, b@berkeley.edu'
+    expect(mail.header[:x_original_bcc].value).to eq 'c@berkeley.edu, d@berkeley.edu'
+  end
+end