Move extract_files to proper test file

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: José Valim

lib/logger/test/logger/utils_test.exs

@@ -100,8 +100,4 @@ defmodule Logger.UtilsTest do
     time = {12, 30, 10, 10}
     assert format_time(time) == ["12", ?:, "30", ?:, "10", ?., [?0, "10"]]
   end
-
-  test "extract_files/2 with empty string returns empty list" do
-    assert extract_files([""], ".ex") == []
-  end
 end

lib/mix/test/mix/utils_test.exs

@@ -33,6 +33,11 @@ defmodule Mix.UtilsTest do
     assert Path.basename(hd(files)) == "local.sample.ex"
   end
 
+
+  test "extract files with empty string returns empty list" do
+    assert Mix.Utils.extract_files([""], ".ex") == []
+  end
+
   test "extract stale" do
     time = {{2030, 1, 1}, {0, 0, 0}}
     assert Mix.Utils.extract_stale([__ENV__.file], [time]) == []