RSpec: Fail any spec typed with a String, not a Symbol

spec_helper.rb

=begin
It's easy to mistakenly say:

    describe 'my feature', type: 'feature' do
      ...
    end
    
...when you really mean:

    describe 'my feature', type: :feature do
    end

The problems start when parts of the system - your code, or gem code -
starts making choices based on that value. If they silently expect it 
to be a Symbol, it'll be a hard problem to troubleshoot.

So let's fail noisily and save ourselves the trouble.
=end

RSpec.configure do |config|
  config.before(:each) do |example|
    example_type = example.metadata[:type]
    if example_type && !example_type.is_a?(Symbol)
      raise "Spec at #{example.location} has a type that is NOT a Symbol: #{example_type.inspect}"
    end
  end
end