No, a vaccination was not always known as not possible. It still isn't, in fact.
And amazing amounts of effort are being spent to make the administration of tests easier. The first tests required trained research technicians. Today tests are still not widespread because they require specialized machinery or other materials. If it were possible to pee on a stick as a self test, everyone would be ecstatic - but it's not, so far.
The pandemic planning stuff I've read from before this year seems to suffer from a number of assumptions that were violated by covid, from asymptomatic transmission to the long lead time. E.g in MERS or Ebola or even flu, the infectious but asymptomatic period is more like Contagion. You don't have to worry about infected people wandering around town for a week or two.
Most planning mentions the need for having tests, and quickly gathering materials etc, and then moves on to tactics for containment and vaccine development. Where testing is focused on, it's as a way to differentiate between people who have symptoms but are actually infected with a non-panfemic disease, so that resources aren't wasted quarantining them. I haven't yet found a scenario studied with a long lead time and possible low level or asymptomatic presentation as standard.