TST add a test for pivot table large number of levels causing int32 overflow

Author: anhqle

pandas/tests/reshape/test_pivot.py

@@ -1276,6 +1276,14 @@ def test_pivot_string_func_vs_func(self, f, f_numpy):
                                aggfunc=f_numpy)
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.slow
+    def test_pivot_number_of_levels_larger_than_int32(self):
+        # GH 20601
+        data = DataFrame({'ind1': list(range(1337600)) * 2,
+                          'ind2': list(range(3040)) * 2 * 440, 'count': [1] * 2 * 1337600})
+        with tm.assert_raises_regex(ValueError, 'int32 overflow'):
+            data.pivot_table(index='ind1', columns='ind2', values='count', aggfunc='count')
+
 
 class TestCrosstab(object):