COMPAT: compare platform return on 32-bit (pandas-dev#18090)

xref pandas-dev#18047

Author: jreback

pandas/tests/test_algos.py

@@ -1243,13 +1243,21 @@ def test_groupsort_indexer():
     result = libalgos.groupsort_indexer(a, 1000)[0]
 
     # need to use a stable sort
+    # np.argsort returns int, groupsort_indexer
+    # always returns int64
     expected = np.argsort(a, kind='mergesort')
+    expected = expected.astype(np.int64)
+
     tm.assert_numpy_array_equal(result, expected)
 
     # compare with lexsort
+    # np.lexsort returns int, groupsort_indexer
+    # always returns int64
     key = a * 1000 + b
     result = libalgos.groupsort_indexer(key, 1000000)[0]
     expected = np.lexsort((b, a))
+    expected = expected.astype(np.int64)
+
     tm.assert_numpy_array_equal(result, expected)