code: def test_add_delta_funsor():
      x = Variable("x", Reals[3])
      y = Variable("y", Reals[3])
      d = Delta("x", y)
  
      expr = -(1 + x**2).log()
      assert d + expr is d + expr(x=y)
      assert expr + d is expr(x=y) + d
  
file_path: funsor/test/test_delta.py
imports: import pytest
  import funsor.ops
  from funsor.delta import Delta
  from funsor.domains import Real, Reals
  from funsor.tensor import Tensor, numeric_array
  from funsor.terms import Number, Variable
  from funsor.testing import assert_close, check_funsor, randn
label_desc: Use image node_id 3 for calling a global function with example usage: test_add_delta_funsor() without return types