How to write regression tests for custom Chef resources?

Given the minimal example

# resources/novowel.rb
resource_name :novowel
property :name, String, name_property: true, regex: /\A[^aeiou]\z/

I would like to write the unit tests in spec/unit/resources/novowel_spec.rb

Resource 'novowel' for name should accept 'k'
Resource 'novowel' for name should accept '&'
Resource 'novowel' for name should NOT accept 'a'
Resource 'novowel' for name should NOT accept 'mm'

to ensure that the name property still works correctly even if the regex is changed for some reason.

I browsed several top notch Chef cookbooks but could not find references for such testing.

How can it be done? Feel free to provide more complex examples with explicitly subclassing Chef::Resource if that helps achieve the task.

Update 1: Could it be that Chef does NOT FAIL when a property does not fit the regex? Clearly this should not work:

link '/none' do
  owner  'r<oo=t'
  to     '/usr'
end

but chef-apply (12.13.37) does not complain about r<oo=t not matching owner_valid_regex. It simply converges as if owner would not have been provided.

Solution

We wrap the DSL inside a little Ruby in order to know the name of the resource's Ruby class:

# libraries/no_vowel_resource.rb
require 'chef/resource'

class Chef
  class Resource
    class NoVowel < Chef::Resource
      resource_name :novowel
      property :letter, String, name_property: true, regex: /\A[^aeiou]\z/
      property :author, String, regex: /\A[^aeiou]+\z/
    end
  end
end

and now we can use RSpec with

# spec/unit/libraries/no_vowel_resource_spec.rb
require 'spec_helper'

require_relative '../../../libraries/no_vowel_resource.rb'

describe Chef::Resource::NoVowel do
  before(:each) do
    @resource = described_class.new('k')
  end

  describe "property 'letter'" do
    it "should accept the letter 'k'" do
      @resource.letter = 'k'
      expect(@resource.letter).to eq('k')
    end

    it "should accept the character '&'" do
      @resource.letter = '&'
      expect(@resource.letter).to eq('&')
    end

    it "should NOT accept the vowel 'a'" do
      expect { @resource.letter = 'a' }.to raise_error(Chef::Exceptions::ValidationFailed)
    end

    it "should NOT accept the word 'mm'" do
      expect { @resource.letter = 'mm' }.to raise_error(Chef::Exceptions::ValidationFailed)
    end
  end

  describe "property 'author'" do
    it "should accept a String without vowels" do
      @resource.author = 'cdrngr'
      expect(@resource.author).to eq('cdrngr')
    end

    it "should NOT accept a String with vowels" do
      expect { @resource.author = 'coderanger' }.to raise_error(Chef::Exceptions::ValidationFailed)
    end
  end
end