async: remove AsyncWriter

we are not expecting real-time problems on the sender's side.

tests/test_async.py

@@ -22,49 +22,9 @@ def test_async_reader():
     r.close()
 
 
-def test_async_write():
-    result = []
-
-    def _write(buf):
-        time.sleep(len(buf) * 0.1)
-        result.append(buf)
-    s = mock.Mock()
-    s.write = _write
-    w = async.AsyncWriter(s)
-
-    w.write('foo')
-    w.write(' ')
-    w.write('bar')
-    w.close()
-    assert w.stream is None
-    w.close()
-    assert result == ['foo', ' ', 'bar']
-
-
 def test_async_reader_error():
     s = mock.Mock()
     s.read.side_effect = IOError()
     r = async.AsyncReader(s, 1)
     with pytest.raises(IOError):
         r.read(3)
-
-
-def test_async_writer_error():
-    s = mock.Mock()
-    s.write.side_effect = IOError()
-    w = async.AsyncWriter(s)
-    w.write('123')
-    w.thread.join()
-    with pytest.raises(IOError):
-        w.write('456')
-    assert s.write.mock_calls == [mock.call('123')]
-
-
-def test_underflow():
-    s = mock.Mock()
-    w = async.AsyncWriter(s)
-    w.write('blah')
-    w.thread.join()
-    assert s.write.mock_calls == [mock.call('blah')]
-    with pytest.raises(IOError):
-        w.write('xyzw')