COMPAT: empty IntervalIndexis np.int64 dtype

xref #19022

Author: jreback

pandas/tests/indexes/interval/test_interval.py

@@ -140,7 +140,7 @@ def test_constructors_nan(self, closed, data):
         np.array([], dtype='datetime64[ns]')])
     def test_constructors_empty(self, data, closed):
         # GH 18421
-        expected_dtype = getattr(data, 'dtype', np.intp)
+        expected_dtype = getattr(data, 'dtype', np.int64)
         expected_values = np.array([], dtype=object)
         expected_index = IntervalIndex(data, closed=closed)