Adds a spec for the mailer password reset view

Updates the mailers/devise_mailer spec with
tests for the password reset view.

spec/mailers/devise_mailer_spec.rb

@@ -94,4 +94,36 @@ RSpec.describe DeviseMailer do
       is_expected.to have_link(Gitlab.config.gitlab.url)
     end
   end
+
+  describe '#reset_password_instructions' do
+    subject { described_class.reset_password_instructions(user, 'faketoken') }
+
+    let_it_be(:user) { create(:user) }
+
+    it_behaves_like 'an email sent from GitLab'
+    it_behaves_like 'it should not have Gmail Actions links'
+    it_behaves_like 'a user cannot unsubscribe through footer link'
+
+    it 'is sent to the user' do
+      is_expected.to deliver_to user.email
+    end
+
+    it 'has the correct subject' do
+      is_expected.to have_subject 'Reset password instructions'
+    end
+
+    it 'greets the user' do
+      is_expected.to have_body_text /Hello, #{user.name}!/
+    end
+
+    it 'includes the correct content' do
+      is_expected.to have_text /Someone, hopefully you, has requested to reset the password for your GitLab account on #{Gitlab.config.gitlab.url}/
+      is_expected.to have_body_text /If you did not perform this request, you can safely ignore this email./
+      is_expected.to have_body_text /Otherwise, click the link below to complete the process./
+    end
+
+    it 'includes a link to reset the password' do
+      is_expected.to have_link("Reset password", href: "#{Gitlab.config.gitlab.url}/users/password/edit?reset_password_token=faketoken")
+    end
+  end
 end