diff --git a/tests/mmm/test_delayed_saturated_mmm.py b/tests/mmm/test_delayed_saturated_mmm.py
index d0a6b644e..b65df3c89 100644
--- a/tests/mmm/test_delayed_saturated_mmm.py
+++ b/tests/mmm/test_delayed_saturated_mmm.py
@@ -106,29 +106,24 @@ def mmm_with_fourier_features() -> DelayedSaturatedMMM:
     )
 
 
-def mmm_with_prior_as_posterior(
-    mmm: DelayedSaturatedMMM, X: pd.DataFrame
-) -> DelayedSaturatedMMM:
-    mmm.sample_prior_predictive(X, samples=2000, extend_idata=True, random_seed=rng)
-    mmm.idata.add_groups({"posterior": mmm.idata.prior})
-
-    return mmm
-
-
 @pytest.fixture(scope="module")
 def mmm_fitted(
-    mmm: DelayedSaturatedMMM,
-    toy_X: pd.DataFrame,
+    mmm: DelayedSaturatedMMM, toy_X: pd.DataFrame, toy_y: pd.Series
 ) -> DelayedSaturatedMMM:
-    return mmm_with_prior_as_posterior(mmm, toy_X)
+    mmm.fit(X=toy_X, y=toy_y, target_accept=0.8, draws=3, chains=2)
+    return mmm
 
 
 @pytest.fixture(scope="module")
 def mmm_fitted_with_fourier_features(
     mmm_with_fourier_features: DelayedSaturatedMMM,
     toy_X: pd.DataFrame,
+    toy_y: pd.Series,
 ) -> DelayedSaturatedMMM:
-    return mmm_with_prior_as_posterior(mmm_with_fourier_features, toy_X)
+    mmm_with_fourier_features.fit(
+        X=toy_X, y=toy_y, target_accept=0.8, draws=3, chains=2
+    )
+    return mmm_with_fourier_features
 
 
 class TestDelayedSaturatedMMM: