If you're going to have weapons like this, you're better off knowing whether and how well they work, and how they can be used. Even if it's only for the threat, the threat has to be 100% credible.

Before the first nuclear test, no less than 3 independent studies were conducted to investigate whether a nuclear explosion could cause a runaway reaction that ignited all or most of earth's atmospheric oxygen. All three studies came to a negative conclusion, but it was serious enough that Oppenheimer reportedly ordered other scientists to stop making jokes about it in the days preceding the first nuclear test, because they were upsetting the non-scientists.

Until you test it, you don't really know what'll happen. And if you don't really know, your enemy doesn't really know. And if your enemy doesn't really know, they might try to fuck around and find out.

If it helps you sleep at night, we stopped testing altogether under the Comprehensive Test Ban Treaty in the 90's.