When using bundler with a project in general and Rails specifically, you have access only to gems defined in your Gemfile. While this makes sense, it can be limiting. Mostly I find it limiting when I want to use a certain RSpec formatter that the rest of the team doesn't use. Unless it's in the Gemfile, it isn't accessible.

Any way around it or I have to add it to Gemfile?

Update: my problem wasn't Bundler but Spork. When running RSpec without Spork I had no problem of using whatever formatter I wanted.