test_all.rb

#!/usr/bin/env ruby

require 'yaml'

rails_versions = ["6.1.0.rc1", "6.0.3.4 ", "5.2.4.4", "5.1.7", "5.0.7.2"].flat_map {|spec| Array(spec).collect {|v| v.gsub /.0(\d)/, '.\\1'}}
rails_envs = YAML.load(File.read("test/database.yml")).keys

rails_versions.each do |version|
  puts "*"*40
  system "RAILS_VERSION=#{version} bundle update" or exit(1)

  rails_envs.each do |env|
    puts "Rails #{version}, #{env}"
    system "RAILS_ENV=#{env} bundle exec rake" or exit(2)
  end
end