py3k buffered IO - flush() required between read/write?

[Genstein]

On 11/05/2011 19:24, Terry Reedy wrote:
> writing and reading. If you want others to look at this more, you should
> 1) produce a minimal* example that demonstrates the questionable
> behavior, and 2) show the comparative outputs that raise your question.

Thanks for a quick response. Perhaps I was being unclear - in py3k, 
given the following code and assuming no errors arise:

 > f = open("foo", "w+b")
 > f.write(b'test')
 > f.seek(0)
 > print(f.read(4))

What is the printed result supposed to be?

i) b'test'
ii) never b'test'
iii) platform dependent/undefined/other

All the best,

	-eg.