Resolves to a consensus of credible sources.

Doesn't have to occur on US soil, as long as it is the US conducting the test. A US test conducted in conjunction with another nation (like France or the UK) would qualify, as long as it's clear that the US is an equal partner in these tests.

By tests, we're talking actual nuclear tests, the kinds we made treaties about, not the kind of monitoring that the US does regularly, even if Trump, say, calls that a "nuclear test".

Very strong OSINT arguments (radioactivity monitoring, seismology, etc) such that a reasonable Manifolder would conclude it is highly likely that the US conducted a nuclear test based on the evidence would qualify, even if the mainstream press phrases things ambiguously like "The US may or may not have conducted a nuclear test" or similar.

I will not bet on this market to remain as objective as possible.