try deepcopy again

arviz/tests/helpers.py

@@ -1,5 +1,6 @@
 """Test helper functions."""
 from collections import OrderedDict
+from copy import deepcopy
 import os
 import pickle
 import sys
@@ -234,7 +235,11 @@ def pystan_noncentered_schools(data, draws, chains):
         stan_model = pystan.StanModel(model_code=schools_code)
         fit = stan_model.sampling(data=data, iter=draws, warmup=0, chains=chains)
     else:
-        stan_model = pystan.build(schools_code, data=data)
+        # PyStan3 bug
+        data_ = {}
+        for k, v in data.items():
+            data_[k] = deepcopy(v)
+        stan_model = pystan.build(schools_code, data=data_)
         fit = stan_model.sample(
             num_chains=chains, num_samples=draws, num_warmup=0, save_warmup=False
         )