diff --git a/test/basic_signup_whitelist_test.exs b/test/basic_signup_whitelist_test.exs
index 36d6904..6c452d0 100644
--- a/test/basic_signup_whitelist_test.exs
+++ b/test/basic_signup_whitelist_test.exs
@@ -2,7 +2,16 @@ defmodule BasicSignupWhitelistTest do
   use ExUnit.Case
   doctest BasicSignupWhitelist
 
+  defp allow_signups_for(whitelist) do
+    System.put_env("SIGNUP_ALLOWED_EMAILS", whitelist)
+  end
+
   test "When not set, not whitelisted" do
-    assert BasicSignupWhitelist.mail_whitelisted("joe@example.com") == false
+    refute BasicSignupWhitelist.mail_whitelisted("joe@example.com")
+  end
+
+  test "When set to star, whitelisted" do
+    allow_signups_for("*")
+    assert BasicSignupWhitelist.mail_whitelisted("joe@example.com")
   end
 end