KAFKA-18834: Fix LoggingResourceTest#testSetLevelDefaultScope

[apalan60]

Jira: KAFKA-18834

• Flaky behavior
  LoggingResourceTest#testSetLevelDefaultScope sometimes fails by not
  capturing its expected WARN log.

• Root cause
  Both LoggersTest#testSetLevelWithValidRootLoggerNames and
  LoggingResourceTest#testSetLevelDefaultScope may share the same
  LoggerContext when executed in the same JVM.
  LoggersTest#testSetLevelWithValidRootLoggerNames calls
  loggers.setLevel("", ERROR), which mutates the global root logger
  level to ERROR and suppresses WARN logs, which causes subsequent tests
  to fail to emit WARN-level output.

• Fix in this PR
  Resets the Log4j configuration after each test in LoggersTest,
  ensuring that any global changes are reverted.

Reviewers: Chia-Ping Tsai chia7712@gmail.com

[apalan60]

Verified that this change resolves the issue by running the following command:

./gradlew cleanTest \
  connect:runtime:test \
  --tests LoggersTest.testSetLevelWithValidRootLoggerNames \
  --tests LoggingResourceTest.testSetLevelDefaultScope \
  -PmaxParallelForks=1

Both tests passed successfully:
LoggersTest#testSetLevelWithValidRootLoggerNames
LoggingResourceTest#testSetLevelDefaultScope

Test Results

kafka on  KAFKA-18834-Fix-LoggingResourceTest#testSetLevelDefaultScope- [$!] …
➜ ./gradlew cleanTest \
  connect:runtime:test \
    --tests LoggersTest.testSetLevelWithValidRootLoggerNames \
    --tests LoggingResourceTest.testSetLevelDefaultScope \
    -PmaxParallelForks=1 \

> Configure project :
Starting build with version 4.1.0-SNAPSHOT (commit id 82ea9d0f) using Gradle 8.14.1, Java 21 and Scala 2.13.16
Build properties: ignoreFailures=false, maxParallelForks=1, maxScalacThreads=8, maxTestRetries=0
Java HotSpot(TM) 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended

> Task :connect:runtime:test

Gradle Test Run :connect:runtime:test > Gradle Test Executor 19 > LoggersTest > testSetLevelWithValidRootLoggerNames() PASSED

Gradle Test Run :connect:runtime:test > Gradle Test Executor 19 > LoggingResourceTest > testSetLevelDefaultScope() PASSED

BUILD SUCCESSFUL in 2s
153 actionable tasks: 2 executed, 151 up-to-date

[chia7712]

This changes all 'child' loggers, right? If so, it is not a kind of restoring logger levels

[apalan60]

@chia7712
Thank you for catching this!

After rethinking the solution, I confirmed that calling setLevel in LoggersTest will overwrite every child loggers (see [1]). That means any test in LoggersTest that invokes setLevel risks leaking its changes into other test classes.

Instead of recording and restoring each logger's previous level, reloading the Log4j configuration after each test may be a simpler solution. This ensures that any global Log4j configuration changes made in LoggersTest are fully reset, and that the restored configuration matches what other tests would see when run independently, which maintains proper test isolation.

I’ve updated the teardown to call LoggerContext.getContext(false).reconfigure(). Please let me know if you have any further feedback!

[apalan60]

I ran a few more test classes that use logging with the command below. They all passed successfully when executed in the same JVM.

./gradlew cleanTest \
-- :connect:runtime:test --tests "LoggersTest.testSetLevelWithValidRootLoggerNames" \
-- :core:test --tests "kafka.network.SocketServerTest"
- PmaxParallelForks=1 

./gradlew cleanTest \
  :connect:runtime:test \
    --tests "LoggersTest.testSetLevelWithValidRootLoggerNames" \
    --tests "LoggingResourceTest" \
    -PmaxParallelForks=1

./gradlew cleanTest \
  :connect:runtime:test --tests "LoggersTest.testSetLevelWithValidRootLoggerNames" \
  :core:test --tests "kafka.network.SocketServerTest" \
  -PmaxParallelForks=1

[chia7712]

Please add comments for this reconfigure

[apalan60]

@chia7712

Sorry for the late update, I've added the comments.