code: def test_set_seasonality_mode(self, backend):
      # Setting attribute
      m = Prophet(stan_backend=backend)
      assert m.seasonality_mode == "additive"
      m = Prophet(
          seasonality_mode="multiplicative", stan_backend=backend
      )
      assert m.seasonality_mode == "multiplicative"
      with pytest.raises(ValueError):
          Prophet(seasonality_mode="batman", stan_backend=backend)
  
imports: import numpy
  import pandas
  import pytest
  from prophet import Prophet
  from prophet.utilities import warm_start_params
label_desc: Use image node_id 6 for calling the TestProphetSeasonalComponent obj's underlying member method code with example usage: obj.test_set_seasonality_mode(backend) without return types