Well, everything is simple, of course, very simple. It can be seen that the master class is for quite newcomers. But I'll lie if I say that I did not learn anything new. Perhaps these are the minuses of self-learning - knowledge is not systematized and comprehensive, there are gaps that can only be filled with practice.
If you have any problem with gem shoulda-matcher after installation and start of gem Zeus, do not just roll back the entire development and say goodbye to Zeus.
Try the following:
gem 'shoulda-matchers', require: false
In file spec/rails_helper.rb if presents, or in spec/spec_helper.rb:
require 'rspec/rails' require 'shoulda/matchers'
It should work. Good luck!