Q: battery tested fine, car won't start

One way to diagnose this is to use a voltmeter to check for battery voltage at the starter motor when the key is held in the "start" position. If there is power to the starter motor, and yet it doesn’t operate, the starter is usually the fault although there could still be a scenario where there is excessive voltage drop and that has to be tested for, as well. If there is no power at all, it has to be confirmed that any engine immobilizer (security) system is de-activated (and thus not a cause of no power). Once that is confirmed, the starter circuit has to be traced to find the fault causing no power delivery to the starter. Such faults are typically wire breaks, faulty fuses, faulty ignition switch, relay, ground and so forth. if you desire that the problem be resolved by a certified mechanic, the recommended service to request is a no start diagnostic. If you request that diagnostic, the problem you are presenting is usually resolved quickly.