'Given the value C{modifiedSince} for the I{If-Modified-Since} header or
the value C{etag} for the I{If-Not-Match} header, verify that a response
with a 200 code, a default Content-Type, and the resource as the body is
returned.'

def _modifiedTest(self, modifiedSince=None, etag=None):

    if (modifiedSince is not None):
        validator = ('If-Modified-Since:    ' + modifiedSince)
    else:
        validator = ('If-Not-Match:    ' + etag)
    for line in ['GET    /    HTTP/1.1', validator, '']:
        self.channel.dataReceived((line + '\r\n'))
    result = self.transport.getvalue()
    self.assertEqual(httpCode(result), http.OK)
    self.assertEqual(httpBody(result), 'correct')
    self.assertEqual(httpHeader(result, 'Content-Type'), 'text/html')
