Adding test case for concat OrderedDict and updating . pandas-dev#21510

Author: SaturninoMateus

doc/source/whatsnew/v0.23.2.txt

@@ -83,4 +83,5 @@ Bug Fixes
 **Other**
 
 - Bug in :meth:`Series.nlargest` for signed and unsigned integer dtypes when the minimum value is present (:issue:`21426`)
--
+- Bug in :class:`_Concatenator` should not sort Ordered Dictionaries (:issue:21510`)
+-

pandas/tests/reshape/test_concat.py

@@ -1,3 +1,4 @@
+from collections import OrderedDict
 from warnings import catch_warnings
 from itertools import combinations, product
 
@@ -1294,6 +1295,16 @@ def test_concat_rename_index(self):
         tm.assert_frame_equal(result, exp)
         assert result.index.names == exp.index.names
 
+    def test_concat_with_ordered_dict(self):
+        # GH 21510
+        ps = pd.concat(OrderedDict([('First', pd.Series(range(3))),
+                                    ('Another', pd.Series(range(4)))]))
+        ps_list = list(ps.keys())
+        exp_list = [('First', 0), ('First', 1), ('First', 2),
+                    ('Another', 0), ('Another', 1),
+                    ('Another', 2), ('Another', 3)]
+        assert ps_list == exp_list
+
     def test_crossed_dtypes_weird_corner(self):
         columns = ['A', 'B', 'C', 'D']
         df1 = DataFrame({'A': np.array([1, 2, 3, 4], dtype='f8'),