Resources

parallel_tests - https://github.com/grosser/parallel_tests
database_cleaner - https://github.com/DatabaseCleaner/database_cleaner
Source - https://github.com/driftingruby/104-speeding-up-tests

Summary

Gemfilegroup :development, :test do
  ...
  gem 'parallel_tests'
  gem 'database_cleaner'
end

config/database.ymltest:
  <<: *default
  database: db/test<%= ENV['TEST_ENV_NUMBER'] %>.sqlite3

spec/support/database_cleaner.rb# Don't forget to add the below comment to your rails_helper.rb
# require 'support/database_cleaner' or 
# Dir[Rails.root.join('spec/support/**/*.rb')].each { |f| require f }

RSpec.configure do |config|
 
  config.before(:suite) do
    DatabaseCleaner.clean_with(:truncation)
  end
 
  config.before(:each) do
    DatabaseCleaner.strategy = :transaction
  end
 
  config.before(:each, type: :feature) do
    DatabaseCleaner.strategy = :truncation
  end
 
  config.before(:each) do
    DatabaseCleaner.start
  end
 
  config.after(:each) do
    DatabaseCleaner.clean
  end
 
end