func newUnitToolWaiter(u *state.Unit) *toolsWaiter {
w := u.Watch()
waiter := &toolsWaiter{
changes: make(chan struct{}, 1),
watcher: w,
tooler: u,
}
go func() {
for _ = range w.Changes() {
waiter.changes <- struct{}{}
}
close(waiter.changes)
}()
return waiter
}