code: def step_join(self):
      # we can't easily account for the number of foreach splits,
      # so we only care about unique lineages (hence set())
      self.lineage = (
          tuple(sorted({x.lineage for x in inputs})),
          self._current_step,
      )
  
imports: from metaflow_test import MetaflowTest, ExpectationFailed, steps
label_desc: Use image node_id 2 for calling the LineageTest obj's underlying member method code with example usage: obj.step_join() without return types