code: def test_cg_errors(self):
      A = lambda x: x
      b = jnp.zeros((2,))
      with self.assertRaisesRegex(
          ValueError, "x0 and b must have matching tree structure"
      ):
          jax.scipy.sparse.linalg.cg(A, {"x": b}, {"y": b})
      with self.assertRaisesRegex(
          ValueError, "x0 and b must have matching shape"
      ):
          jax.scipy.sparse.linalg.cg(A, b, b[:, np.newaxis])
      with self.assertRaisesRegex(
          ValueError, "must be a square matrix"
      ):
          jax.scipy.sparse.linalg.cg(jnp.zeros((3, 2)), jnp.zeros((2,)))
      with self.assertRaisesRegex(
          TypeError,
          "linear operator must be either a function or ndarray",
      ):
          jax.scipy.sparse.linalg.cg([[1]], jnp.zeros((1,)))
  
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 7 for calling the LaxBackedScipyTests obj's underlying member method code with example usage: obj.test_cg_errors() without return types