Library functions in Inspec Test

Question

Team --

I have a ruby library helper in which I have defined multiple functions/methods. How do I reference those in Chef Inspec tests?

def interface_name
  # some code with logic
end

In my specific use case, I am checking to see if a custom networking device was specified as a JSON parameter, and if it was, I am validating it make sure its real (incase they misspelled it) and also gathering its IP and state and other data as reported by Ohai

This is what I have so far, but I'm not sure if this is correct

  describe file('/path/to/custom_attributes.json') do
    it { should exist }
    unless json('/path/to/custom_attributes.json').empty? do
      its(['networking']['interface_name']) { should_not be_empty }
      interface_name = file(json('/path/to/custom_attributes.json').params['networking']['interface_name'])
    end
  end

  describe file('/etc/NetworkManager/system-connections/wired_connection') do
    unless interface_name.empty?
      its('content') { should_not match(/^interface-name=wl.*/mx) }
    end
    its('content') { should match(%r{ca-cert=/etc/ssl/certs/ca-certificates\.crt}mx) }
    its('content') { should match(/id=\.corp.*type=ethernet.*autoconnect-priority=100.*dns-search=corp\.domain.com.*/mx) }
  end
end

The problem / question is that if I gather the parameter directly from the JSON file, then I am bypassing all the validation logic that I'm doing in the library, which defeats the purpose. So, how do I get access to that library function/method in the Inspec test?

For reference, here is the function:

def interface_name
  file = '/path/to/custom_attributes.json'
  if File.exist?(file) && !File.stat(file).zero?
    attributes = JSON.parse(File.read(file))
    device_name = attributes['networking']['interface_name']
    if device_name && !device_name.empty? && networking_devices.include?(device_name)
      interface = device_name
      Chef::Log.info("Valid custom interface provided, using \"#{device_name}\".")
    else
      Chef::Log.debug("Invalid interface (\"#{device_name}\") provided. Valid options are: \"#{networking_devices.keys}\"")
      interface = nil
    end
  else
    Chef::Log.debug('No custom interface provided.')
  end
  interface
rescue JSON::ParserError
  nil
end