gistfile1.rb

class Foo
end

class Foobar < Foo
end

describe 'foo' do
  it 'works weird' do
    Foo.should_receive(:new)

    Foobar.new
  end
end

I'd expect that to pass. Here's why:

• When you mock or stub a method rspec defines that method on the given object (Foo, in this case), so that it can respond to that message based on how you've configured it (e.g. and_return, and_raise, etc).
• There's no definition of Foobar.new, so when Foobar receives the new message, it goes up the ancestor chain to find a definition.
• Normally it would find Class#new, but because Foo.new exists now, it finds that first, and executes it.

I can see why this would be confusing, but hopefully that makes sense.