RFR: 8295814: jdk/jshell/CommandCompletionTest.java fails with "lists don't have the same size expected [2] but found [1]"

[Adam Sotona]

File completion in CommandCompletionTest::testSet intermittently fails.
Also message provided by org.testng.Assert::assertEquals is also not very verbose when comparing collections:
"lists don't have the same size expected [2] but found [1]".

Cause of the failure is in the expected side of the assertion (CommandCompletionTest::getRootDirectories), which may conatain duplicates. While the actual side of the assertion is distinct (CommandCompletionTest::computeCompletions).

Proposed patch de-duplicates CommandCompletionTest::getRootDirectories and adds full description of the expected result to the error message for future debugging.

Please review.

Thanks,
Adam

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Commit messages:
 - CommandCompletionTest removed from ProblemList
 - Merge branch 'master' into JDK-8295814
 - 8295814: jdk/jshell/CommandCompletionTest.java fails with "lists don't have the same size expected [2] but found [1]"

Changes: https://git.openjdk.org/jdk/pull/10870/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10870&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295814
  Stats: 5 lines in 2 files changed: 2 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10870.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10870/head:pull/10870

PR: https://git.openjdk.org/jdk/pull/10870