I'm with JW.
Launch the boat, put it alongside a pontoon, securely tie it up and run it up gently at first. You can then slowly build the engine speed and see if the engine is happy.
You probably won't want to use full throttle with the boat alongside but will be able to load up the engine and make it work without the risk of having to row home.
This will put more load on the engine than running free so will be a good test.
If all goes well you can then take a trip further out.
No prizes for blowing it up and having to be "assisted" / "rescued"