adding a test testing explicitly for stability

Author: realead

pandas/tests/libs/test_hashtable.py

@@ -272,6 +272,14 @@ def test_value_count(self, dtype, type_suffix, writable):
         tm.assert_numpy_array_equal(np.sort(keys), expected)
         assert np.all(counts == 5)
 
+    def test_value_count_stable(self, dtype, type_suffix, writable):
+        value_count = get_ht_function("value_count", type_suffix)
+        values = np.array([2, 1, 5, 22, 3, -1, 8]).astype(dtype)
+        values.flags.writeable = writable
+        keys, counts = value_count(values, False)
+        tm.assert_numpy_array_equal(keys, values)
+        assert np.all(counts == 1)
+
     def test_duplicated_first(self, dtype, type_suffix, writable):
         N = 100
         duplicated = get_ht_function("duplicated", type_suffix)