Cloud Run integration tests within Cloud Build steps?

I am looking at what Cloud Run suggests for local testing here, which is to docker run your
container, and then run your tests against it on localhost:8080. Something like this:

PORT=8080 && 
docker run -d -p 8080:${PORT} -e PORT=${PORT} gcr.io/myproject/myimage && 
./runtests.sh

Now let’s say I want to run these tests as part of a Cloud Build. Is it possible/advisable to run docker run as a Cloud Build step? I don’t see any gcr.io image for docker itself, so I’m guessing not?

Or does it need to be actually deployed to Cloud Run first, then tested?

Source: StackOverflow