Add go_file_name test

Author: sue445

_tools/ruby_h_to_go/spec/ruby_h_to_go/generator_helper_spec.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+RSpec.describe RubyHToGo::GeneratorHelper do
+  include RubyHToGo::GeneratorHelper
+
+  describe "#go_file_name" do
+    subject { go_file_name(header_dir:, ruby_header_file:) }
+
+    let(:header_dir) { "/path/to/include" }
+    let(:ruby_header_file) { "/path/to/include/ruby/internal/intern/thread.h" }
+
+    it { should eq "ruby-internal-intern-thread.go" }
+  end
+end