Cannot load 'pry' - `require': cannot load such file -- pry (LoadError)

I'm trying to debug a simple ruby console script and am getting a load error when trying to require pry:

• I'm using rbenv to management environment.
• I'm using Ruby version: 2.3.1.
• Trying to use Pry '~> 0.10.4'

/Users/gangelo/.rbenv/versions/2.3.1/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- pry (LoadError)

I've used Pry and Byebug in the past in rails applications and never had any issues like this. Searching for a solution, I've found that most issues are related to either not including Pry in the Gemfile or not including the Pry gem in the correct environment in the Gem file; this isn't the case with me, what am I doing wrong?

# /Gemfile
group :development, :test do
  gem 'pry', '~> 0.10.4'
end

And in my script:

# /calculator/rpn_calculator_service.rb
module RealPage
  module Calculator
    # Provides Reverse Polish Notation computation services.
    class RPNCalculatorService < CalculatorService
      include Helpers::Arrays

      def initialize
        super RPNInputParser.new
      end

      def compute(input)
        # Load error here :(
        require 'pry'; binding.pry
        # Code removed for brevity...
      end
      # Code removed for brevity...
    end
  end
end