Extract pure executor of koans

lib/execute.ex

@@ -0,0 +1,48 @@
+defmodule Execute do
+  def run_module(module) do
+    run_until_failure(module, &run_koan/2)
+  end
+
+  def run_until_failure(module, callback) do
+    Enum.reduce_while(module.all_koans, :passed, fn(it, _acc) ->
+      result = callback.(module, it)
+      if result == :passed do
+        {:cont, :passed}
+      else
+        {:halt, result}
+      end
+    end)
+  end
+
+  def run_koan(module, name, args \\ []) do
+    parent = self()
+    spawn fn -> exec(module, name, args, parent) end
+    receive do
+      :ok   -> :passed
+      error -> {:failed, error, module, name}
+    end
+  end
+
+  def exec(module, name, args, parent) do
+    result = apply(module, name, args)
+    send parent, expand(result)
+    Process.exit(self(), :kill)
+  end
+
+  def expand(:ok), do: :ok
+  def expand(error) do
+    {file, line} = System.stacktrace
+      |> Enum.drop_while(&in_ex_unit?/1)
+      |> List.first
+      |> extract_file_and_line
+
+      %{error: error, file: file, line: line}
+  end
+
+  defp in_ex_unit?({ExUnit.Assertions, _, _, _}), do: true
+  defp in_ex_unit?(_), do: false
+
+  defp extract_file_and_line({_, _, _, [file: file, line: line]}) do
+   {file, line}
+  end
+end