BUG: Concat with inner join and empty DataFrame

Author: abaldenko

doc/source/whatsnew/v0.20.0.txt

@@ -570,7 +570,7 @@ Bug Fixes
 - Bug in ``pd.read_csv()`` with ``float_precision='round_trip'`` which caused a segfault when a text entry is parsed (:issue:`15140`)
 
 - Bug in ``DataFrame.to_stata()`` and ``StataWriter`` which produces incorrectly formatted files to be produced for some locales (:issue:`13856`)
-
+- Bug in ``pd.concat()`` in which empty dataframe with ``join='inner'`` was being improperly handled (:issue:`15328`)
 
 
 
@@ -579,6 +579,4 @@ Bug Fixes
 - Bug in ``DataFrame.boxplot`` where ``fontsize`` was not applied to the tick labels on both axes (:issue:`15108`)
 - Bug in ``Series.replace`` and ``DataFrame.replace`` which failed on empty replacement dicts (:issue:`15289`)
 - Bug in ``pd.melt()`` where passing a tuple value for ``value_vars`` caused a ``TypeError`` (:issue:`15348`)
-- Bug in ``.eval()`` which caused multiline evals to fail with local variables not on the first line (:issue:`15342`)
-
-- Bug in ``pd.concat()`` in which empty dataframe with ``join='inner'`` was being improperly handled (:issue:`15328`)
+- Bug in ``.eval()`` which caused multiline evals to fail with local variables not on the first line (:issue:`15342`)

pandas/tests/tools/test_concat.py

@@ -1829,12 +1829,11 @@ def test_concat_inner_join_empty(self):
         # GH 15328
         df_empty = pd.DataFrame()
         df_a = pd.DataFrame({'a': [1, 2]}, index=[0, 1], dtype='int64')
-        result = pd.concat([df_empty, df_a], axis=1, join='inner')
-        expected = pd.DataFrame({'a': []}, index=[], dtype='int64')
-        assert_frame_equal(result, expected)
+        df_expected = pd.DataFrame({'a': []}, index=[], dtype='int64')
 
-        result = pd.concat([df_a, df_empty], axis=1, join='inner')
-        assert_frame_equal(result, expected)
+        for how, expected in [('inner', df_expected), ('outer', df_a)]:
+            result = pd.concat([df_a, df_empty], axis=1, join=how)
+            assert_frame_equal(result, expected)
 
     def test_concat_series_axis1_same_names_ignore_index(self):
         dates = date_range('01-Jan-2013', '01-Jan-2014', freq='MS')[0:-1]