code: def test_override_n_changepoints(self, daily_univariate_ts, backend):
      train = daily_univariate_ts.head(20).copy()
      m = Prophet(n_changepoints=15, stan_backend=backend)
      history = m.setup_dataframe(train, initialize_scales=True)
      m.history = history
      m.set_changepoints()
      assert m.n_changepoints == 15
      cp = m.changepoints_t
      assert cp.shape[0] == 15
  
imports: import numpy
  import pandas
  import pytest
  from prophet import Prophet
  from prophet.utilities import warm_start_params
label_desc: Use image node_id 11 for calling the TestProphetTrendComponent obj's underlying member method code with example usage: obj.test_override_n_changepoints(daily_univariate_ts, backend) without return types