'L{server.Request} within the proxy sets certain response headers by
default. When we get these headers back from the remote server, the
defaults are overridden rather than simply appended.'

def test_defaultHeadersOverridden(self):

    request = self.makeRequest('foo')
    request.responseHeaders.setRawHeaders('server', ['old-bar'])
    request.responseHeaders.setRawHeaders('date', ['old-baz'])
    request.responseHeaders.setRawHeaders('content-type', ['old/qux'])
    client = self.makeProxyClient(request, headers={'accept': 'text/html'})
    self.connectProxy(client)
    headers = {'Server': ['bar'], 'Date': ['2010-01-01'], 'Content-Type': ['application/x-baz']}
    client.dataReceived(self.makeResponseBytes(200, 'OK', headers.items(), ''))
    self.assertForwardsResponse(request, 200, 'OK', list(headers.items()), '')
