boom.rb

# Run this with rspec 2 or 3, it will randomly fail in ruby 2.3.0-preview2 when the ".new" example runs last.
# It fails with
#    1) SmallCircle .new
#     Failure/Error:
#       def area
#         super(2)
#
#     ArgumentError:
#       wrong number of arguments (given 1, expected 0)
#       inline_spec.rb:23:in `area'
#       inline_spec.rb:24:in `area'
#       inline_spec.rb:38:in `block (2 levels) in <main>'
#
# Maybe something in here doesn't like ruby 2.3.0-preview2: https://github.com/rspec/rspec-mocks/blob/master/lib/rspec/mocks/any_instance/recorder.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rspec', ">= 3"
end

require 'rspec'
require 'rspec/autorun'

class Shape
  def area(value)
    value
  end
end

class Circle < Shape
  def area
    super(2)
  end
end

class SmallCircle < Circle
end

RSpec.describe SmallCircle do
  it "stub method, then .new" do
    allow_any_instance_of(described_class).to receive(:area).and_return(1)
    expect(described_class.new.area).to eq 1
  end

  it ".new" do
    p described_class.instance_method(:area)
    expect(described_class.new.area).to eq 2
  end
end

Variation also has the same problem with minitest-stub_any_instance: https://gist.github.com/jrafanie/5f45ce478a024621ff14