Vehicle ran fine yesterday. Today it wouldn't

REPLACE YOUR PMC POWER RELAY IN YOUR FUSE BOX.

Usually a sign of something draining the battery.
The machine test probably showed the battery could hold a charge and the alternator was charging the battery.
You may need to have someone check for a power drain.
When the key switch is off, there may be a weak short to ground or a relay or component that is using power.

No danger involved, just useless. If ONE vehicle won't jump it, there's something drastically wrong with the engine. A charging system will only charge a max of 14 volts when charging a low or dead battery. Over that will hurt something. If you have two vehicles connected to your low battery, there's still only 14 volts going out from them and into yours. There is no reason why one jump vehicle won't charge and start your vehicle. Unless of course the jumped battery is really bad or has a bad/dirty connection. So clean your terminals before a jump. You may not need a jump.

check the battery for full charge, you should have a minimum of 12.4 volts, once its charged ( I'd have a parts store do a LOAD test on it ) start the vehicle, and check the posts again, it should be giving you a reading of 13.5 to 14.5 volts,, if not, and you've cleaned all the contacts you have a bad alternator

I'd start with a battery first. Sounds like the battery has 1 or more dead cells in it. the battery may have all the volts you could want but if it doesn't have the proper amperage it won't crank the motor. You can have the battery load tested for free at Auto Zone or Advance Auto. A simple down and dirty test would be to disconnect the Positive cable and jump the vehicle by connecting directly to that and a good ground on the block. The motor should turn over as long as the vehicle you use as a jump has the proper amperage in it's battery. If the vehicle starts then it is the battery, if it doesn't then you need to look at the starter and other components.

check alternator belts, it might be loose or missing, if you can get it started one more time, while the vehicle is running detach the positive battery cable from the positive battery post. if car goes dead the alternator needs to be replaced because it is probably bad.

click and no turn over is the starting system. battery, starter and solenoid, ignition switch. if batt is fully charged, check that cables are clean and tight. loose cables can start the vehicle sometimes and not others.

earth cable from body to engine and battery to chassis ,clean the connections and fit an additional cable ,also clean and grease the battery terminal

Bad Starter...easy