Nice idea but clearly an amateur.
You are, but thanks for admitting it.
I am too - well except I have been paid to develop circuitry that while it has perfectly legitimate purposes (managing lighting in a public area based on certain inputs) it could easily be altered to trigger a bomb (instead of turning the lights on it closes the detonator circuit).
To test for jamming.. Swipe your finger across the screen, bring finger to mouth, taste substance. If it tastes like Raspberry then you've been jammed.
Another method that may be more palatable to these types.. Can you receive your control signal? If yes, you're not being jammed. If no, assume jamming.
To protect the person placing the bomb (assuming this is desired - it is not always the case, in fact many people have been sent out unknowingly with bombs intended to explode at a predetermined time, place, or by a remote control) - when you detect you cannot detect your control signal you start a 10 minute countdown. Or 5 minutes. Or 1 minute.
You could even start with the timer, and have the control signal reset it. No control pulse within allotted timeframe, then a bomb's gotta do what a bomb's gotta do - "let there be light!"
As to testing? You see if the software closes the relay (or in any other way sends the trigger pulse along the wires to the detonator) at the right time. That can be achieved by the incredibly difficult task of turning off the transmitter while the detonator is on your test bench and seeing if the right volts gets to the right places (you could even fit an actual detonator and stand back far enough - if it does what it is supposed to do you have achieved your result). If it does, it works. If it doesn't, fix it.
You can cover the 'going through a tunnel' bit by 1) avoiding tunnels or 2) not arming the device until you actually have it in place, or perhaps by 3) using a timer rather than an instant trigger (though 2 is probably the best way to handle that situation).
And yes, I have built or modified devices intended to detonate a small fuel/air explosion in a precisely timed manner. It's called an ignition system on a car. I've also designed circuits to manage lighting under pre-determined conditions.
My knowledge of explosives like C4 comes from movies, where a small metallic object with wires on it is stuck in the lump of C4. This is attached to a device that I assume supplies a certain amount of voltage to the object. Whether the object then explodes, heats up, or emits electricity in some fashion I don't know I understand C4 needs a charge to go on but again - I watch movies I don't research explosives. But I don't really need to know the chemistry behind a bomb, all I need is a way to give it a trigger and a way to convert electricity into that trigger. I'll bet I can ignite a match with a bit of wire wrapped around the head. I'll bet the same principle would work with funpowder, blackpowder and probably several other substances that get a little excited when they get warmed up.
Oh, and on final setup, if you're worried about wiring.. A little lamp/LED you wire across the detonator, a switch that bypasses the detonator, and a way to make the trigger "active" to trigger the light (instead of the bomb).