Error is raised if an answer isn't provided for each koan

test/test_helper.exs

@@ -3,10 +3,22 @@ ExUnit.start()
 defmodule TestHarness do
   def test_all(module, answers) do
     module.all_koans
+    |> check_answer_count(answers, module)
     |> Enum.zip(answers)
     |> run_all(module)
   end
 
+  defp check_answer_count(koans, answers, module) do
+    koans_count = length(koans)
+    answer_count = length(answers)
+
+    if length(koans) > length(answers) do
+      raise "Answer missing for #{module}. #{koans_count} koans, but only #{answer_count} answers."
+    else
+      koans
+    end
+  end
+
   def run_all(pairs, module) do
     Enum.map(pairs, fn ({koan, answer}) -> Execute.run_koan(module, koan, [answer]) end)
   end