Add test gems

Author: sue445

ruby_header_parser.gemspec

@@ -36,6 +36,10 @@ Gem::Specification.new do |spec|
   # Uncomment to register a new dependency of your gem
   # spec.add_dependency "example-gem", "~> 1.0"
 
+  spec.add_development_dependency "rspec-its"
+  spec.add_development_dependency "rspec-parameterized"
+  spec.add_development_dependency "rspec-temp_dir"
+
   # For more information and examples about making a new gem, check out our
   # guide at: https://bundler.io/guides/creating_gem.html
 end