add minutest to development group in Gemfile

.gitignore

@@ -16,3 +16,4 @@ server.rb
 *.sw?
 /tmp/
 /_yardoc/
+.idea/

Gemfile

 source "https://rubygems.org"
 
 gemspec
+
+group :development do
+  gem 'minitest', '~> 5.8', '>= 5.8.4'
+end