class_docstr: Generic abstract class for a test dataset 
class_docstr_tok: ["Generic","abstract","class","for","a","test","dataset"]
docstr: the constructor should set the following fields: 
docstr_tok: ["the","constructor","should","set","the","following","fields",":"]
code: def __init__(self):
      """the constructor should set the following fields:"""
      self.d = -1
      self.metric = "L2"  # or IP
      self.nq = -1
      self.nb = -1
      self.nt = -1
  
imports: import os
  import numpy
  import faiss
  from .vecs_io import fvecs_read, ivecs_read, bvecs_mmap, fvecs_mmap
  from .exhaustive_search import knn
label_desc: Use image node_id 1 to create a new Dataset object  with example: obj = Dataset()