code: def output_spec(self) -> dict[str, lit_types.LitType]:
      return {
          "score": lit_types.RegressionScore(),
          "grad_class": lit_types.CategoryLabel(
              required=False, vocab=[]
          ),
          "tokens": lit_types.Tokens(),
          "tokens_sentence1": lit_types.Tokens(
              parent="sentence1", required=False
          ),
          "token_grad_sentence1": lit_types.TokenGradients(
              align="tokens_sentence1",
              grad_for="input_embs_sentence1",
              grad_target_field_key="grad_class",
          ),
          "tokens_sentence2": lit_types.Tokens(
              parent="sentence2", required=False
          ),
          "token_grad_sentence2": lit_types.TokenGradients(
              align="tokens_sentence2",
              grad_for="input_embs_sentence2",
              grad_target_field_key="grad_class",
          ),
      }
  
imports: from typing import Optional
  from absl.testing import absltest
  from absl.testing import parameterized
  from lit_nlp.api import dataset
  from lit_nlp.api import model
  from lit_nlp.api import types
  from lit_nlp.components import hotflip
  from lit_nlp.lib import utils
  import numpy
label_desc: Use image node_id 2 for calling the TestRegressionModel obj's underlying member method code with example usage: obj.output_spec() and returns: dict