code: def test_default(self):
      self._register_factory("platform_A", 20)
      self._register_factory("platform_B", 10)
  
      backend = xb.get_backend()
      self.assertEqual(backend.platform, "platform_A")
      # All backends initialized.
      self.assertEqual(len(xb._backends), len(xb._backend_factories))
  
imports: import os
  import platform
  import time
  import warnings
  from absl import logging
  from absl.testing import absltest
  from jax._src import compiler
  from jax._src import config
  from jax._src import test_util
  from jax._src import xla_bridge
  from jax._src.interpreters import xla
  from jax._src.lib import xla_client
label_desc: Use image node_id 7 for calling the GetBackendTest obj's underlying member method code with example usage: obj.test_default() without return types