code: def test_function():
      """
      test the function function in tf_util
      """
      with tf.Graph().as_default():
          x_ph = tf.placeholder(tf.int32, (), name="x")
          y_ph = tf.placeholder(tf.int32, (), name="y")
          z_ph = 3 * x_ph + 2 * y_ph
          linear_fn = function([x_ph, y_ph], z_ph, givens={y_ph: 0})
  
          with single_threaded_session():
              initialize()
  
              assert linear_fn(2) == 6
              assert linear_fn(2, 2) == 10
  
imports: import numpy
  import tensorflow
  from stable_baselines.common.tf_util import function, initialize, single_threaded_session, is_image
label_desc: Use image node_id 1 for calling a global function with example usage: test_function() without return types