minitestの依存関係(?)問題をbundlerで解決する

プロを目指す人のためのRuby入門の第3章のminitestのところで、以下のようなテストクラスを用意するところがあります。

# fizz_buzz_test.rb

require 'minitest/autorun'

class FizzBuzzTest < Minitest::Test
    def test_fizz_buzz
        assert_equal'1', fizz_buzz(1)
        assert_equal'2', fizz_buzz(2)
        assert_equal'Fizz', fizz_buzz(3)
    end
end

環境によっては以下のようなエラーに遭遇する場合があります。

k-3:lib k$ ruby fizz_buzz_test.rb
/usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems/specification.rb:2291:in `raise_if_conflicts': Unable to activate railties-5.1.6, because activesupport-5.2.1 conflicts with activesupport (= 5.1.6) (Gem::ConflictError)
        from /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems/specification.rb:1411:in `activate'
        from /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems.rb:220:in `rescue in try_activate'
        from /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems.rb:213:in `try_activate'
        from /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:126:in `rescue in require'
        from /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:40:in `require'
        from /usr/local/lib/ruby/gems/2.4.0/gems/railties-5.1.6/lib/minitest/rails_plugin.rb:2:in `<top (required)>'
        from /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
        from /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
        from /usr/local/lib/ruby/gems/2.4.0/gems/minitest-5.11.3/lib/minitest.rb:98:in `block in load_plugins'
        from /usr/local/lib/ruby/gems/2.4.0/gems/minitest-5.11.3/lib/minitest.rb:92:in `each'
        from /usr/local/lib/ruby/gems/2.4.0/gems/minitest-5.11.3/lib/minitest.rb:92:in `load_plugins'
        from /usr/local/lib/ruby/gems/2.4.0/gems/minitest-5.11.3/lib/minitest.rb:121:in `run'
        from /usr/local/lib/ruby/gems/2.4.0/gems/minitest-5.11.3/lib/minitest.rb:63:in `block in autorun'

これで解決できます！（本質的な解決ではない）

bundlerを使うことで、Gemfileで指定したバージョンのminitestを実行できる。

gem install bundler
bundle init

Gemfileが作られるので、Gemfileに追記します。

# Edit Gemfile
gem 'minitest'

bundle install
bundle exec ruby fizz_buzz_test.rb