The Department of Energy has released a video of a subcritical nuclear test.
A subcritical test results in no yield and would be permissable, even under a comprehensive test ban. Subcritical tests are used to determine the physical properties of fissile materials.
Of course, subcritical tests can raise suspicion, as Wolfgang Panofsky has noted, that a country is conducting concealable low yield testing. In 1997, Russian subcritical experiments appear to have coincided with an earthquake, leading to claims that Russia was conducting clandestine low-yield tests.
The decision to publish a film of a subcritical test is one that I think should be commended, rather than subject to demonstration.
Suzanne Jones and Frank Von Hippel proposed some transparency measures for subcritical tests.