code: def testEmptyReservoir(self):
      r = reservoir.Reservoir(1)
      self.assertFalse(r.Keys())
  
imports: import tensorflow
  from tensorboard.backend.event_processing import reservoir
label_desc: Use image node_id 1 for calling the ReservoirTest obj's underlying member method code with example usage: obj.testEmptyReservoir() without return types