Add more specific tests

pandas/core/dtypes/concat.py

@@ -92,11 +92,13 @@ def _get_frame_result_type(result, objs):
     if all blocks are SparseBlock, return SparseDataFrame
     otherwise, return 1st obj
     """
+
+    from pandas.core.sparse.api import SparseDataFrame
+
     if result.blocks and all(b.is_sparse for b in result.blocks):
-        from pandas.core.sparse.api import SparseDataFrame
         return SparseDataFrame
     else:
-        return objs[0]
+        return next(obj for obj in objs if not type(obj) == SparseDataFrame)
 
 
 def _concat_compat(to_concat, axis=0):

pandas/tests/sparse/test_combine_concat.py

@@ -337,23 +337,24 @@ def test_concat_sparse_dense(self, fill_value):
         exp = pd.concat([self.dense3, self.dense1], axis=1)
         # See GH18914 and #18686 for why this should be
         # A DataFrame
-        assert isinstance(res, pd.DataFrame)
+        assert type(res) is pd.DataFrame
         # See GH16874
-        assert res.isnull()
-        assert res[res.columns[0]]
-        assert res.iloc[0,0]
+        assert not res.isnull().empty
+        assert not res[res.columns[0]].empty
+        assert res.iloc[0,0] == self.dense3.iloc[0,0]
+
         for column in self.dense3.columns:
             tm.assert_series_equal(res[column], exp[column])
 
         tm.assert_frame_equal(res, exp)
 
         res = pd.concat([sparse, self.dense3], axis=1)
         exp = pd.concat([self.dense1, self.dense3], axis=1)
-        assert isinstance(res, pd.DataFrame)
+        assert type(res) is pd.DataFrame
         # See GH16874
-        assert res.isnull()
-        assert res[res.columns[0]]
-        assert res.iloc[0,0]
+        assert not res.isnull().empty
+        assert not res[res.columns[0]].empty
+        assert res.iloc[0,0] == sparse.iloc[0,0]
         for column in self.dense3.columns:
             tm.assert_series_equal(res[column], exp[column])
         tm.assert_frame_equal(res, exp)