refining CountryColumnsMergerTest

src/CountryColumnsMerger.py

@@ -5,12 +5,6 @@ class CountryColumnsMerger:
 
     @staticmethod
     def mergeCountryColumnOfSrcIntoDst(src: pd.DataFrame, dst: pd.DataFrame):
-        def merge(series):
-            if pd.isnull(series['COUNTRY_dst']):
-                return series['COUNTRY_src']
-            else:
-                return series['COUNTRY_dst']
-
         merged = pd.merge(
             dst,
             src,
@@ -18,6 +12,23 @@ class CountryColumnsMerger:
             left_index = True,
             right_index = True,
             suffixes=('_dst', '_src'))
-        merged['COUNTRY'] = merged.apply(merge, axis = 'columns').astype('string')
+        merged['COUNTRY'] = (merged
+                                .apply(
+                                    lambda series: CountryColumnsMerger._merge(
+                                                        series['COUNTRY_src'],
+                                                        series['COUNTRY_dst']),
+                                    axis = 'columns')
+                                .astype('string'))
         return merged.drop(columns = ['COUNTRY_dst', 'COUNTRY_src'])
+    
+    @staticmethod
+    def _merge(src, dst):
+        if (CountryColumnsMerger._isNonUnique(src, dst)) or (pd.isnull(src) and pd.isnull(dst)):
+            raise Exception()        
+        
+        return src if not pd.isnull(src) and pd.isnull(dst) else dst
+
+    @staticmethod
+    def _isNonUnique(src, dst):
+        return not pd.isnull(src) and not pd.isnull(dst) and src != dst