code: def _test_fast_inference(self, length):
      with fastmath.use_backend(fastmath.Backend.JAX):
          model_fn = functools.partial(
              ct.ConfigurableTransformerLM,
              vocab_size=16,
              d_model=4,
              d_ff=8,
              n_layers=2,
              n_heads=2,
          )
          batch_size = 2
          inp = np.zeros((batch_size, length), dtype=np.int32)
  
          test_utils.test_eval_equals_predict(inp, model_fn)
  
file_path: trax/trax/models/research/configurable_transformer_test.py
imports: import functools
  from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from trax import fastmath
  from trax import layers
  from trax import shapes
  from trax.layers import test_utils
  from trax.models.research import configurable_transformer
label_desc: Use image node_id 5 for calling the ConfigurableTransformerTest obj's underlying member method code with example usage: obj._test_fast_inference(length) without return types