Refactor some cmd.js logic out into its own file for easier tests

While working on issue #69 I started to come across places where it was a little difficult to test if just a particular flag was called. I think it might help if some of the logic that is in cmd.js is broken out into its own file, so it would be easier to test if a particular flag was specified, and not necessarily test what that flag actually does. That could be done in its own separate test, where it would be easier to mock certain functions.

@richardlau @Trott thoughts?

I can send a PR so we can talk about it also

まず cmd.js を読み、特定の flag が指定されたかどうかを判定するロジックを特定します。そのロジックを独立したファイルに分離し、必要に応じて関数をモックしながら単独でテストできるようにします。各 flag の動作まで同時にテストしない、flag 検出に焦点を当てたテストが用意されれば完了です。