class_docstr: Test various aspects of the directed GrapohSAGE node generator, with the focus
  on the sampled neighbourhoods and the extracted features.
code: def test_one_hop(self):
      # Test 1 in-node and 1 out-node sampling
      self.sample_one_hop(1, 1)
      # Test 0 in-nodes and 1 out-node sampling
      self.sample_one_hop(0, 1)
      # Test 1 in-node and 0 out-nodes sampling
      self.sample_one_hop(1, 0)
      # Test 0 in-nodes and 0 out-nodes sampling
      self.sample_one_hop(0, 0)
      # Test 2 in-nodes and 3 out-nodes sampling
      self.sample_one_hop(2, 3)
  
file_path: stellargraph/tests/mapper/test_directed_node_generator.py
imports: import networkx
  import pandas
  from stellargraph.mapper import DirectedGraphSAGENodeGenerator
  from stellargraph.core.graph import StellarDiGraph
  from ..test_utils.graphs import weighted_tree
label_desc: Use image node_id 2 for calling the TestDirectedNodeGenerator obj's underlying member method code with example usage: obj.test_one_hop() without return types