Elaborate on gem usage?

[doub1ejack]

I'm pretty new to ruby, which is why I want to use simplecov to help keep me on track. That is probably also the reason I don't understand the usage for this gem. I've added the gem to my Gemfile and run bundle update and see that it has been installed.

I'm assuming that each time simplecov runs, a new shield should be generated at coverage/coverage.svg, is that right? I haven't been able to get simplecov-shield to generate that image yet. I've run rspec and guard to generate new simplecov stats and tried this in the console:

$ rails c
Loading development environment (Rails 4.2.3)
irb: warn: can't alias context from irb_context.
2.2.5 :001 > require 'simplecov-shield'
 => true
2.2.5 :002 > SimpleCov.formatter = SimpleCov::Formatter::ShieldFormatter
 => SimpleCov::Formatter::ShieldFormatter

I haven't found any other sites describing how to use this gem yet either. Could you provide some more details?