Once you created your rails application with:
rails new <app_name> -T # to exclude Test::Unit
Add the RSpec gem to your Gemfile in the following way:
group :development, :test do
gem "rspec-rails"
end
In Command line write:
bundle install # this will install the missing gems
Now you need to install RSpec by running:
rails generate rspec:install
This will generate the following files:
create .rspec
create spec
create spec/spec_helper.rb
create spec/rails_helper.rb
I strongly recommended to read through all spec_helper and rails_helper comments to get a good understanding of what each option does.
Once everything is set you can run all your tests with:
bundle exec rspec
You can read more about the recommended spec_helper and rails_helper configurations on https://kolosek.com/rails-rspec-setup.