RFR: Improve testing of GitHub PositionMapper

[Robin Westberg via github.com]

Hi all,

Please review this test of the GitHub PositionMapper (which also found an off-by-one bug).

Best regards,
Robin

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Commits:
 - 760fd776:	Improve testing of GitHub PositionMapper

Pull request:
https://git.openjdk.java.net/skara/pull/43

Webrev:
https://webrevs.openjdk.java.net/skara/43/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/43.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/43/head:pull/43