KAFKA-19947 Add Unit test coverage for KafkaCSVMetricsReporter

[devtrace404]

This PR adds comprehensive unit test coverage for the KafkaCSVMetricsReporter class, which previously had zero test coverage.

Test Results

% ./gradlew :core:test --tests kafka.metrics.KafkaCSVMetricsReporterTest
> Task :core:test

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testCsvFileFormat() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testMultipleStopsAreSafe() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testReporterDoesNotStartWhenDisabled() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testReporterStartsWhenEnabled() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testStopAndRestart() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testManualStart() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testMultipleStartsAreSafe() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testCustomPollingInterval() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testOldDirectoryIsDeleted() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testDirectoryCreation() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testDirectoryCreationWithDefaultPath() PASSED

Gradle Test Run :core:test > Gradle Test Executor 3 > KafkaCSVMetricsReporterTest > testReporterCreationAndMBeanName() PASSED
BUILD SUCCESSFUL in 2m 34s
86 actionable tasks: 86 executed

[github-actions[bot]]

A label of 'needs-attention' was automatically added to this PR in order to raise the attention of the committers. Once this issue has been triaged, the triage label should be removed to prevent this automation from happening again.