It means you have given a word that the kata writer does not consider to be in the input. The most likely explanation is that you have split a word where the writer did not want you to (e.g. splitting "wor'd" into "wor" and "d") or you have joined two or more words that the kata writer considered to be separate. Try printing the input immediately and you should get a better idea what the random tests are like. Only apostrophes can be used to connect letters together into one word.

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The examples given by you seem to be correct.

What exactly you think is wrong, and why?

Python tests work just fine. Closing.

The python tests work for me, and there are almost 14,000 python solutions, so I don't think the tests are the problem.