Backported from: https://github.com/pyamg/pyamg/commit/6f5e549e6105e18cfff9bf4b5f1834d081fa4510
Author: Luke Olson
--- a/pyamg/aggregation/tests/test_smooth.py
+++ b/pyamg/aggregation/tests/test_smooth.py
@@ -485,6 +485,9 @@ class TestEnergyMin(TestCase):
                 Bc = ml.levels[1].B
                 P = ml.levels[0].P.tocsr()
 
+                T.eliminate_zeros()
+                P.eliminate_zeros()
+
                 # P should preserve B in its range, wherever P
                 # has enough nonzeros
                 mask = ((P.indptr[1:] - P.indptr[:-1]) >= B.shape[1])