Migrate log4j-jul to JUnit 5

[AlbaHerrerias]

Hello 👋

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 log4j-jul.

Thank you!

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)

[AlbaHerrerias]

Hi, we are currently blocked and would like your advice. We've found out that the surefire-junit47 provider specified here only executes JUnit 4 tests. We've attempted to change the version and the provider with no luck. Is there another version of this dependency that would set up java.util.logging as required, but will also run JUnit 5 tests? Do you have any pointers for us? Thank you

[ppkarwasz]

@AlbaHerrerias,

The problem with surefire-junit-platform was that either Surefire or JUnit 5 (I don't remember which one) initializes JUL (and therefore Log4j) way before control is transferred to the test class. Therefore this code executes too late:

logging-log4j2/log4j-jul/src/test/java/org/apache/logging/log4j/jul/test/CoreLoggerTest.java

Lines 59 to 62 in 031d4da

	public static void setUpClass() {
	System.setProperty("java.util.logging.manager", LogManager.class.getName());
	System.setProperty(Constants.LOGGER_ADAPTOR_PROPERTY, CoreLoggerAdapter.class.getName());
	}

To workaround that, all the tests must be split into at least 4 Surefire runs, depending on the system properties that they need.
Most test classes require the java.util.logging.manager property to be set (except Log4jBridgeHandlerTest), but some need additional properties.
For example AsyncLoggerThreadsTest additionally needs the log4j2.contextSelector property to be set:

          <execution>
            <id>async-logger-test</id>
            <goals>
              <goal>test</goal>
            </goals>
            <phase>test</phase>
            <configuration>
              <includes>
                <include>**/AsyncLoggerThreadsTest.class</include>
              </includes>
              <!-- Use custom `j.u.l.LogManager` and an asynchronous selector -->
              <systemPropertyVariables>
                <java.util.logging.manager>org.apache.logging.jul.tolog4j.LogManager</java.util.logging.manager>
                <log4j2.contextSelector>org.apache.logging.log4j.core.async.AsyncLoggerContextSelector</log4j2.contextSelector>
              </systemPropertyVariables>
            </configuration>
          </execution>

CoreLoggerTest needs an additional log4j2.julLoggerAdapter system property.