Remove : from mix path helpers to avoid issues on Windows

Author: José Valim

lib/mix/test/test_helper.exs

@@ -61,15 +61,15 @@ defmodule MixTest.Case do
   end
 
   def fixture_path(extension) do
-    Path.join(fixture_path(), extension)
+    Path.join(fixture_path(), extension |> to_string() |> String.replace(":", ""))
   end
 
   def tmp_path do
     Path.expand("../tmp", __DIR__)
   end
 
   def tmp_path(extension) do
-    Path.join(tmp_path(), to_string(extension))
+    Path.join(tmp_path(), extension |> to_string() |> String.replace(":", ""))
   end
 
   def purge(modules) do