system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How do governments and militaries test out nuclear weapons without creating disastrous effects on the environment/ecosystem?

Just like the title says, I don't understand how they can test nuclear bombs in the desert, or Bikini Atoll (in the ocean) without permanently irradiating the ecosystem (and consequently, Earth) beyond repair.

They've tested dozens and dozens of nuclear bombs throughout the years, and I'm confused why that hasn't messed our world up?
gpt
The impact of a single nuclear weapon on the global environment is actually very small, and open air testing during the 1900’s took place in extremely remote locations. That being said, those locations have been damaged in a big way and the effects are still present today. 

A lot of open air tests happened in the early nuclear days. Since then actual testing has been moved to deep underground tests to avoid the issues with fallout, and even underground testing is extremely rare today (North Korea has probably done more live tests than any other nation in decades)

One area of supercomputing has been to simulate and model nuclear weapons performance based on known quantities, which greatly reduced the need for testing in major nations at least. Other than that the expected performance of nuclear weapons is based on analysis more than actual testing. If you look up some history of nuclear tests by the US and USSR in the 1900’s, many had yields that were higher or lower than predicted. That body of testing knowledge is what enables the prediction of yields in modern weapons. 

And since nuclear weapons are complex, it’s possible to test components and subsystems without a full nuclear explosion. That allows the controls, detonators, etc to be tested without the need to obliterate anything big.