class_docstr: Dummy model for testing Model.is_compatible_with_dataset().
code: def output_spec(self) -> types.Spec:
      return {}
  
imports: 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
label_desc: Use image node_id 3 for calling the _CompatibilityTestModel obj's underlying member method code with example usage: obj.output_spec() and returns: dict