class_docstr: Test that the engine registry allows to:
  - select the right engine based on the configuration
  - deal with the typical error cases (unknowns, duplicates, etc)
code: def test_valid_engines(self) -> None:
      engine = get_engine("train")
      assert engine is not None
      assert isinstance(engine, Engine)
  
      engine = get_engine("extract_features")
      assert engine is not None
      assert isinstance(engine, Engine)
  
imports: import unittest
  from vissl.engines.engine_registry import Engine, get_engine, register_engine
label_desc: Use image node_id 1 for calling the TestEngineRegistry obj's underlying member method code with example usage: obj.test_valid_engines() without return types