// object). When `len(partSizes) == 1`, asMultipart is used to upload
// the object as multipart with 1 part or as a regular single object.
//
// All upload failures are considered test errors - this function is
// intended as a helper for other tests.
func uploadTestObject(t *testing.T, apiRouter http.Handler, creds auth.Credentials, bucketName, objectName string,