Add simplecov

Author: darthjee

ruby_gnuplot.gemspec

@@ -18,5 +18,6 @@ Gem::Specification.new do |s|
   s.require_paths = ["lib"]
 
   s.add_development_dependency 'minitest'
-  s.add_development_dependency 'rspec', '3.9.0'
+  s.add_development_dependency 'rspec',     '3.9.0'
+  s.add_development_dependency 'simplecov', '0.17.0'
 end

spec/spec_helper.rb

@@ -13,6 +13,11 @@
 # it.
 #
 # See http://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
+require 'simplecov'
+SimpleCov.start do
+  add_filter '/spec/'
+end
+
 require "gnuplot"
 
 RSpec.configure do |config|