response, err = s.client.Do(request)
	c.Assert(err, nil)
	c.Assert(response.StatusCode, http.StatusPreconditionFailed)

	// make HTTP request to obtain object info.
	// But this time set a date with unrecognized format to the "If-Modified-Since" header
	request, err = newTestSignedRequest(http.MethodHead, getHeadObjectURL(s.endPoint, bucketName, objectName),
		0, nil, s.accessKey, s.secretKey, s.signer)
	c.Assert(err, nil)