code: def _mock_kernel(x1, x2, history, batch=None):
      """A kernel that memorizes its calls and encodes a fixed values for equal/unequal
      datapoint pairs."""
      history.append((x1, x2))
  
      mult = 1.0 if batch is None else np.linspace(1, 5, batch)
  
      if x1 == x2:
          return 1 * mult
      return 0.2 * mult
  
imports: import math
  import sys
  from functools import partial
  import pytest
  import numpy
  import pennylane
  import pennylane.kernels
  from pennylane import numpy
label_desc: Use image node_id 3 for calling a global function with example usage: _mock_kernel(x1, x2, history, batch) and returns: unknown, unknown