[, yxvm, zzozybj, booifcbcs, ...
^^

This, means there is actually an empty string at the first element. And as a matter of fact...:

Empty string values should be ignored.

ok, but i still don't understand this error :(

(unmeaningful message, I need to track a bug...)

and? Don't you see your problem? You printed the input, so you should see what you forgot, considering the requirements.

Thank you for your advice, input is [, yxvm, zzozybj, booifcbcs, w{niq, {{vizzwid]
expected: <[]yxvm, zzozybj, booif...>
but was: <[, ]yxvm, zzozybj, booif...>

Sample tests are just "sample". If you wanna know the input, print it to the console (System.out.println(Arrays.toString(...));)

In that case, the SampleTest would not execute
but i completed all the tasks and no problem with this tests
In randomTest i can show you only the stack trace and expected and actual outputs)

input

...?

Anyway, you're wrong about that, because you're not following this requirement:

formatWords(['ninja', '', 'ronin']) // should return "ninja and ronin"

Thanks for your reply, for example:
expected:<...ba, lsfq, wpfq, bz, [iayrl, za], onga, etpxcjcn, fv...> but was:<...ba, lsfq, wpfq, bz, [, iayrl, za, ], onga, etpxcjcn, fv...>
And also, i noticed some more: (expected and actual outputs)
[] -> [, ]
[etikvlog{, exro], -> [, etikvlog{, exro, ],
[] -> [ and ]

I just did the java version without troubles. Do you have an example of something going wrong? (meaning: input, acutal and expected outputs, what's wrong about the expected one?)

The Java kata still is not working, because randomTests work very strange with some symbols
Below there are mentions of this from the other people