Extract function to get the source file of a module

lib/display.ex

@@ -1,14 +1,12 @@
 defmodule Display do
   alias IO.ANSI
+  @current_dir File.cwd!
 
   def show_failure(%{expr: expr}, module, name) do
-    source = module.__info__(:compile)
-              |> Dict.get(:source)
-              |> Path.relative_to(File.cwd!)
     IO.puts("")
     IO.puts("Now meditate upon #{display_module(module)}")
     IO.puts("---------------------------------------")
-    IO.puts("Assertion failed in #{source}:#{line_number(expr)}")
+    IO.puts("Assertion failed in #{source_file(module)}:#{line_number(expr)}")
     IO.puts(display_koan(name))
     IO.puts(format_red(Macro.to_string(expr)))
   end
@@ -26,6 +24,12 @@ defmodule Display do
     line
   end
 
+  defp source_file(module) do
+    module.__info__(:compile)
+    |> Dict.get(:source)
+    |> Path.relative_to(@current_dir)
+  end
+
   defp format_red(str) do
     Enum.join([ANSI.red, str, ANSI.reset], "")
   end