Add a preview for this mailer

test/mailers/previews/user_mailer_preview.rb

@@ -0,0 +1,18 @@
+class UserMailerPreview < ActionMailer::Preview
+  def email_change_confirmation
+    ApplicationRecord.current_tenant = "897362094"
+    user = User.find_by(email_address: "david@37signals.com") || User.new(
+      name: "David",
+      email_address: "david@37signals.com"
+    )
+
+    new_email_address = "david.new@example.com"
+    token = user.generate_email_address_change_token(to: new_email_address)
+
+    UserMailer.email_change_confirmation(
+      user: user,
+      email_address: new_email_address,
+      token: token
+    )
+  end
+end