atcoder-util-0.3.0 is not a library.
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atcoder-util-0.3.2
atcoder-util make it easy to test for your code in sample cases in competitive programming.
Gen
First, you have to fetch input/output example from AtCoder's website. If you provide only contest name, sample cases of all problem in the contest will be downloaded.
$ atcoder-util gen abc145
Or if you specify a contest name and a problem, sample cases of the problem will be downloaded.
$ atcoder-util gen abc145 c
Test
After you fetched sample cases, you can run check whether its answer is correct in all at once.
$ atcoder-util test c