def test_capabilities():
sio = StringIO()
assert sio.readable()
assert sio.writable()
assert sio.seekable()
assert not sio.isatty()
assert not sio.closed
assert not sio.line_buffering
sio.close()
raises(ValueError, sio.readable)
raises(ValueError, sio.writable)
raises(ValueError, sio.seekable)
raises(ValueError, sio.isatty)
assert sio.closed
assert sio.errors is None
