class Hash

def assert_valid_keys(*valid_keys)

{ name: 'Rob', age: '28' }.assert_valid_keys(:name, :age) # => passes, raises nothing
{ name: 'Rob', age: '28' }.assert_valid_keys('name', 'age') # => raises "ArgumentError: Unknown key: :name. Valid keys are: 'name', 'age'"
{ name: 'Rob', years: '28' }.assert_valid_keys(:name, :age) # => raises "ArgumentError: Unknown key: :years. Valid keys are: :name, :age"

meaning that string and symbol keys will not match.
Note that keys are treated differently than HashWithIndifferentAccess,

+ArgumentError+ on a mismatch.
Validates all keys in a hash match *valid_keys, raising 
def assert_valid_keys(*valid_keys)
  valid_keys.flatten!
  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