tests: add more controller tests.

* Fix an exception in /artists/show_or_new.

test/unit/user_mailer_test.rb

@@ -0,0 +1,38 @@
+require "test_helper"
+
+class UserMailerTest < ActionMailer::TestCase
+  context "UserMailer" do
+    setup do
+      @user = create(:user, email_address: build(:email_address))
+    end
+
+    context "dmail_notice method" do
+      should "work" do
+        @dmail = create(:dmail, owner: @user, to: @user)
+        mail = UserMailer.dmail_notice(@dmail)
+        assert_emails(1) { mail.deliver_now }
+      end
+    end
+
+    context "password_reset method" do
+      should "work" do
+        mail = UserMailer.password_reset(@user)
+        assert_emails(1) { mail.deliver_now }
+      end
+    end
+
+    context "email_change_confirmation method" do
+      should "work" do
+        mail = UserMailer.email_change_confirmation(@user)
+        assert_emails(1) { mail.deliver_now }
+      end
+    end
+
+    context "welcome_user method" do
+      should "work" do
+        mail = UserMailer.welcome_user(@user)
+        assert_emails(1) { mail.deliver_now }
+      end
+    end
+  end
+end