RFR: 8270836: Foolproof JavadocTester.checkOutput [v2]

[Pavel Rappo]

On Fri, 16 Jul 2021 14:44:24 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> When searching output for multiple strings it is easy to misexpress your intent, which could make a failing test pass. Such cases can be caught and reported to the programmer.
>> 
>> For example, for this search to succeed it is sufficient for the output to consist only of the `"error: bad"` string:
>> 
>> 
>> checkOutput(..., "error:", "error: bad", ...)
>
> Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve the test

What's interesting is that this PR caused 17 test failures in tier1, which is more than I had expected. I'll fix those use sites of `checkOutput` and update the PR. Looks like this PR has a good practical value.

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PR: https://git.openjdk.java.net/jdk/pull/4811