RFR: CODETOOLS-7902843: Fix simple test issues found by static analysis

[Aleksey Shipilev]

SonarCloud reports multiple problems in test code. Some of them are legitimate problems that break/weaken the tests.

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Commit messages:
 - CODETOOLS-7902843: Fix simple test issues found by static analysis

Changes: https://git.openjdk.java.net/jcstress/pull/9/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=9&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902843
  Stats: 21 lines in 7 files changed: 0 ins; 6 del; 15 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/9.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/9/head:pull/9

PR: https://git.openjdk.java.net/jcstress/pull/9