code: def test_stack():
      """Test invoking Stack."""
      input1 = np.random.rand(5, 4).astype(np.float32)
      input2 = np.random.rand(5, 4).astype(np.float32)
      result = layers.Stack()([input1, input2])
      assert result.shape == (5, 2, 4)
      assert np.array_equal(input1, result[:, 0, :])
      assert np.array_equal(input2, result[:, 1, :])
  
imports: import deepchem
  import numpy
  import pytest
  import os
label_desc: Use image node_id 4 for calling a global function with example usage: test_stack() without return types