Update Rakefile

Co-authored-by: Sutou Kouhei <[email protected]>

Author: eregon

Rakefile

@@ -22,8 +22,12 @@ else
   task :compile
 end
 Rake::TestTask.new(:test) do |t|
-  ENV["RUBYOPT"] = "-I" + [*(extask.lib_dir if extask), "test/lib"].join(File::PATH_SEPARATOR)
-  t.libs << extask.lib_dir if extask
+  if extask
+    ENV["RUBYOPT"] = "-I" + [extask.lib_dir, "test/lib"].join(File::PATH_SEPARATOR)
+    t.libs << extask.lib_dir
+  else
+    ENV["RUBYOPT"] = "-Itest/lib"
+  end
   t.libs << "test/lib"
   t.ruby_opts << "-rhelper"
   t.test_files = FileList["test/**/test_*.rb"]