code: def subtest(self, d, metric, topk, search_L, threshold):
      metric_names = {
          faiss.METRIC_L1: "L1",
          faiss.METRIC_L2: "L2",
          faiss.METRIC_INNER_PRODUCT: "IP",
      }
      topk = 10
      nt, nb, nq = 2000, 1000, 200
      xt, xb, xq = get_dataset_2(d, nt, nb, nq)
      gt_index = faiss.IndexFlat(d, metric)
      gt_index.add(xb)
      gt_D, gt_I = gt_index.search(xq, topk)
  
      K = 16
      index = faiss.IndexNNDescentFlat(d, K, metric)
      index.nndescent.S = 10
      index.nndescent.R = 32
      index.nndescent.L = K + 20
      index.nndescent.iter = 5
      index.verbose = False
  
      index.nndescent.search_L = search_L
  
      index.add(xb)
      D, I = index.search(xq, topk)
      recalls = 0
      for i in range(nq):
          for j in range(topk):
              for k in range(topk):
                  if I[i, j] == gt_I[i, k]:
                      recalls += 1
                      break
      recall = 1.0 * recalls / (nq * topk)
      print(
          "Metric: {}, L: {}, Recall@{}: {}".format(
              metric_names[metric], search_L, topk, recall
          )
      )
      assert recall > threshold, "{} <= {}".format(recall, threshold)
  
imports: from __future__ import absolute_import, division, print_function
  import unittest
  import faiss
  import numpy
  from common_faiss_tests import Randu10k, get_dataset_2, Randu10kUnbalanced
label_desc: Use image node_id 4 for calling the TestNNDescent obj's underlying member method code with example usage: obj.subtest(d, metric, topk, search_L, threshold) without return types