code: def test_sparse_vectors():
      svs = sparse_vectors()
      assert len(svs) == 0
  
      svs.resize(5)
      for sv in svs:
          assert len(sv) == 0
  
      svs.clear()
      assert len(svs) == 0
  
      svs.extend(
          [
              sparse_vector([pair(1, 2), pair(3, 4)]),
              sparse_vector([pair(5, 6), pair(7, 8)]),
          ]
      )
  
      assert len(svs) == 2
      assert svs[0][0].first == 1
      assert svs[0][0].second == 2
      assert svs[0][1].first == 3
      assert svs[0][1].second == 4
      assert svs[1][0].first == 5
      assert svs[1][0].second == 6
      assert svs[1][1].first == 7
      assert svs[1][1].second == 8
  
      deser = pickle.loads(pickle.dumps(svs, 2))
      assert deser == svs
  
imports: from dlib import pair, make_sparse_vector, sparse_vector, sparse_vectors, sparse_vectorss
  from pytest import approx
label_desc: Use image node_id 3 for calling a global function with example usage: test_sparse_vectors() without return types