CNDB-11460 another fix for cqlsh unicode tests in TestCqlshUnicode

[djatnieks]

CNDB-11460 another fix for cqlsh unicode tests in TestCqlshUnicode - make a second read in read_until to get UTF-8 characters that are split across reads.

What is the issue

The original fix for CNDB-11460 added the ability for the read_tty method to decode UTF-8 characters that get split across reads, by saving a partial buffer when a UnicodeDecodeError happens, and use the partial buffer with the next read. When this happens, read_tty will return '' to the read_until method. The first fix lacked having read_until initiate a second read to read_tty and still failed with an EOFError.

What does this PR fix and why was it fixed

In this PR, the read_until method will make a second call to read_tty (via self.read), allowing read_tty to read another blksize buffer of characters and the chance to decode UTF-8 characters that were split across reads.

To better validate the fix, the test was run locally with a forced blksize = 1 to consistently generate failures and validate that the second read resolves the issue.

Correct me if this is wrong, but afaict our CC CI doesn't have multiplexing capability for cqhsh tests, having separate build parameters in ds-cassandra-build from JVM tests using DSJVMTestRepetitions or DTests using DSDTestRepetitions.

[github-actions]

Checklist before you submit for review

• Make sure there is a PR in the CNDB project updating the Converged Cassandra version
• Use NoSpamLogger for log lines that may appear frequently in the logs
• Verify test results on Butler
• Test coverage for new/modified code is > 80%
• Proper code formatting
• Proper title for each commit staring with the project-issue number, like CNDB-1234
• Each commit has a meaningful description
• Each commit is not very long and contains related changes
• Renames, moves and reformatting are in distinct commits

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-1618 rejected by Butler

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3 new test failure(s) in 1 builds
See build details here

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Found 3 new test failures

Test	Explanation	Branch history	Upstream history
...estInterruptedExceptionCachedCounterLockManager	regression	🔴
...TimeoutTest.prepareRPCTimeout[SEQUENTIAL/false]	regression	🔴	🔵🔵🔵🔵🔵🔵🔵
o.a.c.s.SensorsIndexWriteTest.BeforeFirstTest	regression	🔴

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Found 1 known test failures