code: def test_predict_is_nonconstant():
      """
      We should not really have predictions that are constant (should be some difference)...
      This captures bugs with the predict function not iterating forward
      """
      model = ARIMAX(
          formula="y ~ x1", data=data, ar=2, ma=2, family=Laplace()
      )
      x = model.fit()
      predictions = model.predict_is(h=10, intervals=False)
      assert not np.all(predictions.values == predictions.values[0])
  
imports: import numpy
  import pandas
  from pyflux.arma import ARIMAX
  from pyflux.families import Laplace
label_desc: Use image node_id 9 for calling a global function with example usage: test_predict_is_nonconstant() without return types