starting CountriesMergerTest

src/CountriesMerger.py

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+import pandas as pd
+
+
+class CountriesMerger:
+
+    @staticmethod
+    def mergeCountriesSerieses(countriesSeriesA, countriesSeriesB):
+        return (pd
+                .merge(countriesSeriesA, countriesSeriesB, how='left', left_index=True, right_index=True)
+                .apply(lambda countries: sorted(set(countries.dropna())), axis='columns'))

src/CountriesMergerTest.py

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+import unittest
+import pandas as pd
+from CountriesMerger import CountriesMerger
+from pandas.testing import assert_series_equal
+
+
+class CountriesMergerTest(unittest.TestCase):
+
+    def test_mergeCountriesSerieses(self):
+        # Given
+        countriesSeriesA = pd.Series({'NO72A': 'CountryA-1', 'EW096': 'CountryA-2'}, name='countriesSeriesA')
+        countriesSeriesB = pd.Series({'NO72A': 'CountryB-1', 'FS192': 'CountryB-2'}, name='countriesSeriesB')
+
+        # When
+        mergedCountries = CountriesMerger.mergeCountriesSerieses(countriesSeriesA, countriesSeriesB)
+
+        # Then
+        assert_series_equal(
+            mergedCountries,
+            pd.Series(
+                {
+                    'NO72A': ['CountryA-1', 'CountryB-1'],
+                    'EW096': ['CountryA-2']
+                }))