Uncomment the following line in config/application.rb
require "rails/test_unit/railtie"
and remove rspec from Gemfile.
You will probably have to make a test directory. As well, you will need to add all the relevant details and files from here for all those other things that weren't automagically generated. Check out the latest for Rails testing here:
http://guides.rubyonrails.org/testing.html
mkdir test
cd test
mkdir fixtures functional integration
and so on to make up for the non-generated files.
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Ruby on Rails: Switch from test_unit to rspec