--- a/test/helper.rb
+++ b/test/helper.rb
@@ -80,7 +80,7 @@
     def ruby arg
       Dir.chdir(TEST_DIR) do
         cmd = File.symlink?("/proc/#{$$}/exe") ? File.readlink("/proc/#{$$}/exe") : ENV['_']
-        cmd = "#{cmd} -I #{INC} #{arg} 2>>/tmp/out"
+        cmd = "#{cmd} -I #{INC} #{arg} 2>>#{TEST_DIR}/out.log"
         result = system(cmd)
         result ? assert(result) : raise(cmd)
       end
