def test_children_parents():
rc = Context()
rc.new_value(a=1)
assert len(rc['a'].children) is 0
rc.get_value('a')
assert len(rc['a'].children) is 0
rc.new_observer('b', lambda env: env.a)
rc.run()
assert len(rc['a'].children) is 1
assert len(rc['a'].parents) is 0
assert len(rc['b'].parents) is 1
assert len(rc['b'].children) is 0
