docstr: Check the component is executed exactly once.
code: def assertExecutedOnce(self, component: str) -> None:
      """Check the component is executed exactly once."""
      component_path = os.path.join(self._pipeline_root, component)
      self.assertTrue(fileio.exists(component_path))
      execution_path = os.path.join(
          component_path, ".system", "executor_execution"
      )
      execution = fileio.listdir(execution_path)
      self.assertLen(execution, 1)
  
file_path: tfx/tfx/examples/custom_components/hello_world/example/taxi_pipeline_hello_e2e_test.py
imports: import os
  import tensorflow
  from tfx.dsl.io import fileio
  from tfx.examples.custom_components.hello_world.example import taxi_pipeline_hello
  from tfx.orchestration import metadata
  from tfx.orchestration.beam.beam_dag_runner import BeamDagRunner
label_desc: Use image node_id 2 for calling the TaxiPipelineHelloEndToEndTest obj's underlying member method code with example usage: obj.assertExecutedOnce(component) without return types