minitest_plugin.rb:9 getting wrong number of arguments

This is actually a bug in rails, revealed by minitest update to 5.10.2 as said here and it has already been fixed here.

As the pull request is only 10 hours old (at the time of writing), it has not yet been released, although it's already merged.

In the mean time, you can specify in your Gemfile:

gem 'minitest', '~> 5.10', '!= 5.10.2'

Edit

Don't forget to bundle update minitest

Hey I'm doing this exact tutorial and followed the top solution and it fixed my issue, specifically (for us total noobs) I did this to my Gemfile

group :test do
  gem 'rails-controller-testing', '0.1.1'
  gem 'minitest-reporters',       '1.1.9'
  gem 'guard',                    '2.13.0'
  gem 'guard-minitest',           '2.4.4'
  gem 'minitest', '~> 5.10', '!= 5.10.2' # add this here to fix error
end

It turns out that in my test/test_helper.rb I needed a line of code that was missing. I added this before "class ActiveSupport::TestCase".

    Minitest::Reporters.use!

This gave me a passing result for my test with no strange argument error. Hope this helps someone for the future!