Improve tests for Devise confirmation emails

Recently test coverage was added for the Devise confirmation emails,
but was incomplete. This adds a test context for new users, and adds
important language expectations to the other 2 contexts.

spec/mailers/devise_mailer_spec.rb

@@ -7,10 +7,20 @@ RSpec.describe DeviseMailer do
   describe "#confirmation_instructions" do
     subject { described_class.confirmation_instructions(user, 'faketoken', {}) }
 
+    context "when confirming a new account" do
+      let(:user) { build(:user, created_at: 1.minute.ago, unconfirmed_email: nil) }
+
+      it "shows the expected text" do
+        expect(subject.body.encoded).to have_text "Welcome"
+        expect(subject.body.encoded).not_to have_text user.email
+      end
+    end
+
     context "when confirming the unconfirmed_email" do
       let(:user) { build(:user, unconfirmed_email: 'jdoe@example.com') }
 
-      it "shows the unconfirmed_email" do
+      it "shows the expected text" do
+        expect(subject.body.encoded).not_to have_text "Welcome"
         expect(subject.body.encoded).to have_text user.unconfirmed_email
         expect(subject.body.encoded).not_to have_text user.email
       end
@@ -19,7 +29,8 @@ RSpec.describe DeviseMailer do
     context "when re-confirming the primary email after a security issue" do
       let(:user) { build(:user, created_at: 10.days.ago, unconfirmed_email: nil) }
 
-      it "shows the primary email" do
+      it "shows the expected text" do
+        expect(subject.body.encoded).not_to have_text "Welcome"
         expect(subject.body.encoded).to have_text user.email
       end
     end