Update test.

Author: jverswijver

tests/test_relational_operand.py

@@ -514,3 +514,4 @@ def test_union_multiple():
         x = set(zip(*q1.fetch('i', 'j')))
         y = set(zip(*q2.fetch('i', 'j')))
         assert_set_equal(x, y)
+        assert q1.fetch() == q2.fetch()