code: def test_single_var(self):
      # Test `is_same_graph` with some trivial graphs (one Variable).
  
      x, y, z = vectors("x", "y", "z")
      self.check(
          [
              (x, x, (({}, True),)),
              (
                  x,
                  y,
                  (
                      ({}, False),
                      ({y: x}, True),
                  ),
              ),
              (x, neg(x), (({}, False),)),
              (x, neg(y), (({}, False),)),
          ]
      )
  
file_path: pytensor/tests/graph/rewriting/test_utils.py
imports: from pytensor.graph.fg import FunctionGraph
  from pytensor.graph.rewriting.basic import graph_rewriter
  from pytensor.graph.rewriting.utils import is_same_graph, rewrite_graph
  from pytensor.tensor.math import neg
  from pytensor.tensor.type import vectors
label_desc: Use image node_id 2 for calling the TestIsSameGraph obj's underlying member method code with example usage: obj.test_single_var() without return types