code: def test_kernel_and_bias_defaults():
      gs = GraphSAGE(
          layer_sizes=[4, 4],
          n_samples=[2, 2],
          input_dim=2,
          multiplicity=1,
      )
      for layer in gs._aggs:
          assert isinstance(
              layer.kernel_initializer, tf.initializers.GlorotUniform
          )
          assert isinstance(
              layer.bias_initializer, tf.initializers.Zeros
          )
          assert layer.kernel_regularizer is None
          assert layer.bias_regularizer is None
          assert layer.kernel_constraint is None
          assert layer.bias_constraint is None
  
imports: from tensorflow import keras
  from tensorflow.keras import initializers, regularizers
  import tensorflow
  import numpy
  import pytest
  from stellargraph.mapper import GraphSAGENodeGenerator
  from stellargraph.layer.graphsage import GraphSAGE, MeanAggregator, MaxPoolingAggregator, MeanPoolingAggregator, AttentionalAggregator
  from ..test_utils.graphs import example_graph
  from ..None import test_utils
label_desc: Use image node_id 29 for calling a global function with example usage: test_kernel_and_bias_defaults() without return types