How can I start the rails console and use the testing database exclusively?

in Rails 6 the syntax has changed for this

rails c -e test

You can pass the environment as RAILS_ENV=test:

$ RAILS_ENV=test bundle exec rails console

Or:

$ RAILS_ENV=test bundle exec rails c

You can also do:

$ bundle exec rails console test

Or:

$ bundle exec rails c test

You can see like

Loading test environment (Rails 3.2.8)
1.9.3p327 :001 >

To start console in test environment:

ruby script/console test 
ruby script/console production 

To run rake tasks in test environment:

rake db:create RAILS_ENV=test 
rake db:migrate RAILS_ENV=test 

In Rails 3 and 4 you can use:

rails console test
rails c test

In Rails 5 you can use:

rails console -e test
rails c -e test