fix test

Author: TomeHirata

tests/test_distribution_estimator_base.py

@@ -60,6 +60,7 @@ def fit(self, covariates, treatment_arms, outcomes):
         self.covariates = covariates
         self.treatment_arms = treatment_arms
         self.outcomes = outcomes
+        self.strata = np.zeros(len(covariates))  # Mock strata for QTE testing
 
     def _compute_cumulative_distribution(
         self,