US's Zero-Yield Nuclear Tests - Russia Blamed for Doing Similar?

Lieutenant General Robert Paul Ashley Jr, Director, US DIA, is not saying much when he asserted late May 2019:

"The United States believes that Russia probably is not adhering to its nuclear testing moratorium in a manner consistent with the zero-yield standard."

This is given the US successfully performed a "zero-yield nuclear" tests in Nevada, 2017 to the present day:

“Scientists at Sandia National Laboratories claim to have successfully tested an upgraded version of the B61-12 nuclear bomb.

The US has been working on the B61-12 for several years, and government officials say the latest tests are vital to refurbishing efforts.

An F-16 from Nellis Air Force Base in March successfully dropped a zero-yield version of the bomb over the Nevada desert. It left a "neat hole" and crews were able to dig it out of the dirt for further study.

Sandia Stockpile Resource Center Director Anna Schauer said, "It's great to see things all come together: the weapon design, the test preparation, the aircraft, the range and the people who made it happen."

Scientists will spend the next several months analyzing data gathered from the test flight.

Officials say the US is planning more test flights over the next three years, and the B61-12's first production unit is scheduled to be completed in 2020.

The current B61-12 consolidates and replaces four older versions in the nation's nuclear arsenal.”

Youtube: Testing of the B61-12 nuclear bomb in mid 2018. Narrative kicks in at 20 seconds. Bomb device technical details very interesting from 2 min 37 secs.
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The official legal - technological definitions of nuclear weapons testing are highly complex, ambiguous, even contradictory and include:

“"zero yield" safety tests of warheads, whether the test is successful (there is no nuclear yield) or the test is unsuccessful (there is a nuclear yield). It does not include hydronuclear, cold or subcritical tests because no nuclear explosions are possible, even in failure. In these sorts of tests there may be small amounts of chain reaction occurring, but they stop before materially adding to the chemical explosion that causes them. 

The line here is finely drawn, but, among other things, subcritical testing is not prohibited by the Comprehensive Nuclear Test Ban Treaty, while safety tests are...”

Maybe Russia like all other legal and illegal nuclear nations (India, Pakistan, North Korea, not to mention Israel) continues to conduct “zero-yield” nuclear tests?

Pete