@XFAIL
def test_union_boundary_of_joining_sets():
 assert (Union(Interval(0, 10), Interval(10, 15), evaluate=False).boundary == FiniteSet(0, 15))

@ XFAIL def test_union_boundary_of_joining_sets ( ) : assert ( Union ( Interval ( 0 , 10 ) , Interval ( 10 , 15 ) , evaluate = False ) . boundary == FiniteSet ( 0 , 15 ) )
testing the boundary of unions is a hard problem .