when not defined, not allowed

test/fun_core/basic_signup_whitelist_test.exs

@@ -0,0 +1,11 @@
+defmodule FunCore.BasicSignupWhitelistTest do
+  use ExUnit.Case
+
+  def mail_whitelisted_fun(_signups_allowed, _email_received) do
+    false
+  end
+
+  test "When not set, not whitelisted" do
+    refute(mail_whitelisted_fun(nil, "joe@example.com"))
+  end
+end