BUG: Concat with inner join and empty DataFrame

Author: abaldenko

pandas/tests/tools/test_concat.py

@@ -1825,14 +1825,16 @@ def test_concat_bug_3602(self):
         result = concat([df1, df2], axis=1)
         assert_frame_equal(result, expected)
 
-    def test_concat_bug_15328(self):
+    def test_concat_inner_join_empty(self):
+        # GH 15328
         df_empty = pd.DataFrame()
-        df_a = pd.DataFrame({'a': [1, 2]}, index=[0, 1])
+        df_a = pd.DataFrame({'a': [1, 2]}, index=[0, 1], dtype='int64')
         result = pd.concat([df_empty, df_a], axis=1, join='inner')
-        self.assertTrue(result.empty)
+        expected = pd.DataFrame({'a': []}, index=[], dtype='int64')
+        assert_frame_equal(result, expected)
 
         result = pd.concat([df_a, df_empty], axis=1, join='inner')
-        self.assertTrue(result.empty)
+        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]

pandas/tests/tools/test_merge.py

@@ -54,11 +54,13 @@ def setUp(self):
         self.right = DataFrame({'v2': np.random.randn(4)},
                                index=['d', 'b', 'c', 'a'])
 
-    def test_merge_bug_15328(self):
+    def test_merge_inner_join_empty(self):
+        # GH 15328
         df_empty = pd.DataFrame()
-        df_a = pd.DataFrame({'a': [1, 2]}, index=[0, 1])
+        df_a = pd.DataFrame({'a': [1, 2]}, index=[0, 1], dtype='int64')
         result = pd.merge(df_empty, df_a, left_index=True, right_index=True)
-        self.assertTrue(result.empty)
+        expected = pd.DataFrame({'a': []}, index=[], dtype='int64')
+        assert_frame_equal(result, expected)
 
     def test_merge_common(self):
         joined = merge(self.df, self.df2)