Thank you for your comments. I'll fix the points.

By the way, to test the fork of ```find_or_create``` override, it seems that I have to undef ```Graph``` and ```load``` it again. This is somehow too much.
``` ruby
    context "no additional auto_tagging" do
      let(:path) { 'a/b/c' }
      let(:tag) { 'foo' }
      before {
        Settings.stub(:auto_tagging).and_return(false)
        Object.class_eval do remove_const :Graph end
        load 'app/models/graph.rb'
      }
      subject { Graph.find_or_create(path: path, tag_list: tag) }
      it { expect(subject.tag_list).to eq ([tag]) }
    end
```
Could you tell me the better way if any?