Fix mypy typing and add annotation to the test

Author: makbigc

pandas/core/arrays/integer.py

@@ -1,6 +1,6 @@
 import copy
 import sys
-from typing import Type
+from typing import Tuple, Type
 import warnings
 
 import numpy as np
@@ -512,8 +512,7 @@ def value_counts(self, dropna=True):
 
         return Series(array, index=index)
 
-    #def _values_for_argsort(self) -> np.ndarray:
-    def _values_for_argsort(self):
+    def _values_for_argsort(self) -> Tuple[np.ndarray, np.ndarray]:
         """Return values for sorting.
 
         Returns

pandas/tests/extension/base/methods.py

@@ -45,6 +45,7 @@ def test_argsort_missing(self, data_missing_for_sorting):
         self.assert_series_equal(result, expected)
 
     def test_argsort_nan_loc(self, data_multiple_nan):
+        # GH 21801
         result = data_multiple_nan.argsort()
         expected = np.array([3, 9, 7, 1, 0, 6, 2, 4, 5, 8])
         tm.assert_numpy_array_equal(result, expected)