code: def test_gmres_matmul(self):
      A = CustomOperator(2 * jnp.eye(3))
      b = jnp.arange(9.0).reshape(3, 3)
      expected = b / 2
      actual, _ = jax.scipy.sparse.linalg.gmres(A, b)
      self.assertAllClose(expected, actual)
  
imports: from functools import partial
  import unittest
  from absl.testing import absltest
  import numpy
  import scipy.sparse.linalg
  import jax
  import jax.numpy
  import jax.scipy.sparse.linalg
  from jax import jit
  from jax import lax
  from jax.tree_util import register_pytree_node_class
  import jax._src.scipy.sparse.linalg
  from jax._src import config
  from jax._src import dtypes
  from jax._src import test_util
label_desc: Use image node_id 20 for calling the LaxBackedScipyTests obj's underlying member method code with example usage: obj.test_gmres_matmul() without return types