Switch to use test-unit from minitest

Author: hsbt

Gemfile

@@ -3,7 +3,7 @@ source "https://rubygems.org"
 gemspec
 
 group :development do
-  gem "minitest"
+  gem "test-unit"
   gem "coveralls"
   gem "rubocop"
 end

test/helper.rb

@@ -10,16 +10,15 @@
 rescue Gem::LoadError
 end
 
-gem "minitest", "~> 5"
-require "minitest/autorun"
+require "test/unit"
 require "rake"
 require "tmpdir"
 
 require_relative "support/file_creation"
 require_relative "support/ruby_runner"
 require_relative "support/rakefile_definitions"
 
-class Rake::TestCase < Minitest::Test
+class Rake::TestCase < Test::Unit::TestCase
   include FileCreation
 
   include Rake::DSL