Let's imagine that somehow Iran does figure out how to make a bomb. They are going to need to do tests, and the first bomb is going to be enormous and undeliverable. You can't set off a nuke, even a practice one, without someone knowing. I'm sure we have satellites with sensors to do this exact job. It is impossible for Iran to make a deliverable bomb without at first at least testing one - and that test would be the last thing they ever did. They've already got the radioactive material. Wouldn't a dirty bomb be more effective at ending Israel? Just take your radioactive material, stick in some conventional bombs and irradiate the cities. That's something they could do today if they wanted. Hell, they could give the stuff to IS and let them run around irradiating water supplies and such. I'd be much more worried about that than bomb development, bombs that are probably decades from even being deliverable and the tests would cause an immediate and extreme response. And all of that is under the assumption that Iran is even worth the worry.