Refactor log4j core test

[ninetteadhikari]

Introduction

We are from Neighbourhoodie, the implementation partner of the STF Bug Resilience Program. This work is part of our agreed Milestone 1. Upgrade from JUnit 4 to JUnit 5. This PR migrates the tests located in x to JUnit5.c

Please note the log4j-core-test module contains over 150 files and this PR updates the tests for 40 of them. Further PRs will be made to update the rest of the tests.

Checklist

• Base your changes on 2.x branch if you are targeting Log4j 2; use main otherwise
• ./mvnw verify succeeds (if it fails due to code formatting issues reported by Spotless, simply run ./mvnw spotless:apply and retry)
• Non-trivial changes contain an entry file in the src/changelog/.2.x.x directory
• Tests for the changes are provided
• Commits are signed (optional, but highly recommended)

[github-actions]

Job	Requested goals	Build Tool Version	Build Outcome	Build Scan®
build-macos-latest	clean install	3.9.8	✅
build-ubuntu-latest	clean install	3.9.8	✅
build-windows-latest	clean install	3.9.8	✅

Generated by gradle/develocity-actions

[AlbaHerrerias]

This branch and refactor-log4j-core-test1 (mind the 1) differ in the following files, which I deleted in refactor-log4j-core-test1. I deleted them because they add no value. The changes these files have were introduced before the big JUnit5 automatic refactor not made by us, but after the conflict resolution they ended up looking like this.

log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/OutputStreamAppenderTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/rolling/RollingAppenderOnStartup2Test.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/rolling/RollingAppenderOnStartupDirectTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/async/AsyncLoggerClassLoadDeadlockTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/NestedLoggerConfigTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/convert/DateTypeConverterTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/convert/TypeConverterRegistryTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/convert/TypeConvertersTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/plugins/util/ResolverUtilCustomProtocolTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/layout/JsonLayoutTest.java
log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NameAbbreviatorTest.java