Logging from tools like log4j/slf4j is not captured by TestNG execution

Problem: If someone uses standard logging tool like log4j the messages are not captured by Gradle, hence they don't appear in the test results (html/xml) and they are not passed onto the listeners. (btw. it works just fine for JUnit)

Symptoms:

• some the standard output messages appear in the test results but some of them appear directly in the build log (log4j stuff)
• log4j messages from test execution litter the build log without a way to turn them off

Investigation: For TestNG, we load all the test classes before triggering execution. If the class has a static Logger field (standard style of using a loggin toolkit), the static state gets initialized during class loading (TestNGTestClassProcessor.processTestClass), at this point the log4j initializes loggers and hooks up to the system output / error. Later, the test classes get executed (TestNGTestClassProcessor.stop) and the standard output/error redirector is started (CaptureTestOutputTestResultProcessor.started). However, now it's too late - log4j has already initialized and pushes the output directly to build log.

Possible solutions:

• shuffle the listeners so that we start redirecting early enough. I've tried to spike it but it didn't quite work for me.