Fix Black formatting: add blank line before function definition

Author: uzairgheewala

arviz/tests/base_tests/test_stats.py

@@ -883,6 +883,7 @@ def test_bayes_factor():
     assert bf_dict0["BF10"] > bf_dict0["BF01"]
     assert bf_dict1["BF10"] < bf_dict1["BF01"]
 
+
 def test_compare_sorting_consistency():
     chains, draws = 4, 1000