class RuboCop::Cop::Lint::UnifiedInteger

1.is_a?(Integer)
# good
1.is_a?(Bignum)
1.is_a?(Fixnum)
# bad
@example
Checks for using Fixnum or Bignum constant.

def on_const(node) 

def on_const(node)
  klass = fixnum_or_bignum_const(node)
  return unless klass
  add_offense(node, message: format(MSG, klass: klass)) do |corrector|
    next if target_ruby_version <= 2.3
    corrector.replace(node.loc.name, 'Integer')
  end
end