def test_promise_then():
p = Promise()
d = {}
v = p.then(lambda v: d.setdefault('key', v))
p.resolve('value')
assert v.value == 'value'
assert d['key'] == 'value'
def test_promise_resolve():
p = Promise()
assert p.is_pending
assert not p.is_resolved
assert p.value is None
p.resolve('value')
assert not p.is_pending
assert p.is_resolved
assert p.value == 'value'
with pytest.raises(RuntimeError):
p.resolve('value again')
