code: def test_update(self):
      # Test update mechanism in different settings.
  
      # Simple value assignment.
      x = shared(0)
      assign = pfunc([], [], updates={x: 3})
      assign()
      assert x.get_value() == 3
  
      # Basic increment function.
      x.set_value(0)
      inc = pfunc([], [], updates={x: x + 1})
      inc()
      assert x.get_value() == 1
  
      # Increment by a constant value.
      x.set_value(-1)
      y = shared(2)
      inc_by_y = pfunc([], [], updates={x: x + y})
      inc_by_y()
      assert x.get_value() == 1
  
imports: import numpy
  import pytest
  import pytensor.tensor
  from pytensor.compile import UnusedInputError, get_mode
  from pytensor.compile.function import function, pfunc
  from pytensor.compile.function.pfunc import rebuild_collect_shared
  from pytensor.compile.io import In
  from pytensor.compile.sharedvalue import shared
  from pytensor.configdefaults import config
  from pytensor.graph.utils import MissingInputError
  from pytensor.misc.safe_asarray import _asarray
  from pytensor.tensor.math import sum
  from pytensor.tensor.type import bscalar, bvector, dmatrices, dmatrix, dscalar, dvector, fscalar, fvector, imatrix, iscalar, ivector, ivectors, lscalar, wvector
  from pytensor.utils import PYTHON_INT_BITWIDTH
label_desc: Use image node_id 15 for calling the TestPfunc obj's underlying member method code with example usage: obj.test_update() without return types