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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def run_nested_groups():
 """Run the nested groups example. This example shows a PhaseGroup in a PhaseGroup. No phase is terminal, so all are run in the order; main_phase inner_main_phase inner_teardown_phase teardown_phase """

  test = htf.Test(
      htf.PhaseGroup(
          main=[
              main_phase,
              htf.PhaseGroup.with_teardown(inner_teardown_phase)(
                  inner_main_phase),
          ],
          teardown=[teardown_phase]
      )
  )
  test.execute()