def test_var():
b = BDD()
with nt.assert_raises(AssertionError):
b.var('x')
j = b.add_var('x')
u = b.var('x')
assert u > 0, u
level, low, high = b.succ(u)
assert level == j, (level, j)
assert low == b.false, low
assert high == b.true, high
