Added a special no-extension build to test the code paths without native extensions
diff --git a/lib/rb/Rakefile b/lib/rb/Rakefile
index 53d6096..b4cb9d6 100644
--- a/lib/rb/Rakefile
+++ b/lib/rb/Rakefile
@@ -72,6 +72,7 @@
 desc "Build the native library"
 task :build_ext => :'gen-rb' do
    next if defined?(RUBY_ENGINE) && RUBY_ENGINE =~ /jruby/
+   next if ENV['SKIP_BUILD_EXT'] == '1'
    Dir::chdir(File::dirname('ext/extconf.rb')) do
       unless sh "ruby #{File::basename('ext/extconf.rb')}"
         $stderr.puts "Failed to run extconf"
@@ -115,6 +116,6 @@
 
 CLEAN.include [
   '.bundle', 'benchmark/gen-rb', 'coverage', 'ext/*.{o,bundle,so,dll}', 'ext/mkmf.log',
-  'ext/Makefile', 'ext/conftest.dSYM', 'Gemfile.lock', 'mkmf.log', 'pkg',  'spec/gen-rb',
-  'test', 'thrift-*.gem'
+  'ext/Makefile', 'ext/conftest.dSYM', 'ext/thrift_native.bundle.dSYM', 'mkmf.log',
+  'pkg',  'spec/gen-rb', 'test/debug_proto/gen-rb', 'thrift-*.gem'
 ]