class_docstr: test that the knn search gives the same as distance matrix + argmin 
code: def test_L1(self):
      self.do_test_knn(faiss.METRIC_L1)
  
imports: import numpy
  import faiss
  import unittest
  from common_faiss_tests import get_dataset_2
  import scipy.spatial.distance
label_desc: Use image node_id 2 for calling the TestKNN obj's underlying member method code with example usage: obj.test_L1() without return types