class WebMock::HashValidator

def initialize(hash) 

def initialize(hash)
  @hash = hash
end

def validate_keys(*valid_keys)

This code is based on https://github.com/rails/rails/blob/master/activesupport/lib/active_support/core_ext/hash/keys.rb 
def validate_keys(*valid_keys)
  valid_keys.flatten!
  @hash.each_key do |k|
    unless valid_keys.include?(k)
      raise ArgumentError.new("Unknown key: #{k.inspect}. Valid keys are: #{valid_keys.map(&:inspect).join(', ')}")
    end
  end
end