class NameError

def missing_name

Extract the name of the missing constant from the exception message. 
def missing_name
  if /undefined local variable or method/ !~ message
    $1 if /((::)?([A-Z]\w*)(::[A-Z]\w*)*)$/ =~ message
  end
end

def missing_name?(name)

Was this exception raised because the given name was missing? 
def missing_name?(name)
  if name.is_a? Symbol
    last_name = (missing_name || '').split('::').last
    last_name == name.to_s
  else
    missing_name == name.to_s
  end
end