code: def test_2_couple_terms():
      """
      Tests the length of the latent variable vector for an ARIMAX model
      with 1 AR and 1 MA term, and two predictors, and tests that the values
      are not nan
      """
      model = ARIMAX(
          formula="y ~ x1 + x2", data=data, ar=1, ma=1, family=t()
      )
      x = model.fit()
      assert len(model.latent_variables.z_list) == 7
      lvs = np.array([i.value for i in model.latent_variables.z_list])
      assert len(lvs[np.isnan(lvs)]) == 0
  
imports: import numpy
  import pandas
  from pyflux.arma import ARIMAX
  from pyflux.families import t
label_desc: Use image node_id 19 for calling a global function with example usage: test_2_couple_terms() without return types