Add mailer subject tests and refine i18n keys (#910)

* Add mailer subject tests and refine i18n keys

* Linter

* Fix test

* More fixes

* More fixes

---------

Co-authored-by: sentry[bot] <39604003+sentry[bot]@users.noreply.github.com>
Co-authored-by: Juan José Mata <juanjo.mata@gmail.com>

test/mailers/invitation_mailer_test.rb

@@ -0,0 +1,18 @@
+require "test_helper"
+
+class InvitationMailerTest < ActionMailer::TestCase
+  test "invite_email" do
+    invitation = invitations(:one)
+
+    mail = InvitationMailer.invite_email(invitation)
+
+    assert_equal I18n.t(
+      "invitation_mailer.invite_email.subject",
+      inviter: invitation.inviter.display_name,
+      product_name: Rails.configuration.x.product_name
+    ), mail.subject
+    assert_equal [ invitation.email ], mail.to
+    assert_equal [ "hello@example.com" ], mail.from
+    assert_match "accept", mail.body.encoded
+  end
+end

test/mailers/pdf_import_mailer_test.rb

@@ -9,6 +9,10 @@ class PdfImportMailerTest < ActionMailer::TestCase
   test "next_steps email is sent to user" do
     mail = PdfImportMailer.with(user: @user, pdf_import: @pdf_import).next_steps
 
+    assert_equal I18n.t(
+      "pdf_import_mailer.next_steps.subject",
+      product_name: Rails.configuration.x.product_name
+    ), mail.subject
     assert_equal [ @user.email ], mail.to
     assert_includes mail.subject, "analyzed"
   end