To improve testing, add a layer of indirection around colours.

test/display/failure_test.exs

@@ -5,13 +5,13 @@ defmodule FailureTests do
   test "assertion failure with proper expression" do
     error = error(%ExUnit.AssertionError{expr: "hi"})
 
-   assert Failure.format_failure(error) == "\e[36mAssertion failed in some_file.ex:42\e[0m\n\e[31m\"hi\"\e[0m\n"
+   assert Failure.format_failure(error) == "Assertion failed in some_file.ex:42\n\"hi\"\n"
   end
 
   test "assertion failure with message" do
     error = error(%ExUnit.AssertionError{expr: :ex_unit_no_meaningful_value, message: "hola"})
 
-   assert Failure.format_failure(error) == "\e[36mAssertion failed in some_file.ex:42\e[0m\n\e[31mhola\e[0m\n"
+   assert Failure.format_failure(error) == "Assertion failed in some_file.ex:42\nhola\n"
   end
 
   defp error(error) do

test/display/notification_test.exs

@@ -4,6 +4,6 @@ defmodule NotificationTest do
 
   test "shows possible koans when a koan can not be found" do
     message  = Notifications.invalid_koan(SampleKoan, [PassingKoan])
-    assert message == "Did not find koan SampleKoan in \e[31mPassingKoan\e[0m"
+    assert message == "Did not find koan SampleKoan in PassingKoan"
   end
 end