TST: Add numsum overflow test

Author: Javier Sorribes Camargo

pandas/tests/test_nanops.py

@@ -327,6 +327,12 @@ def test_nansum(self):
         self.check_funs(nanops.nansum, np.sum, allow_str=False,
                         allow_date=False, allow_tdelta=True, check_dtype=False)
 
+    def test_nansum_overflow(self):
+        s = Series([2**31])
+        self.assertEqual(s.sum(),2147483648)
+        s = Series([2**31-1,1])
+        self.assertEqual(s.sum(),2147483648)
+    
     def test_nanmean(self):
         self.check_funs(nanops.nanmean, np.mean, allow_complex=False,
                         allow_obj=False, allow_str=False, allow_date=False,