@Override
      public Void answer(InvocationOnMock invocation) throws Throwable {
        org.apache.logging.log4j.core.LogEvent logEvent =
          invocation.getArgument(0, org.apache.logging.log4j.core.LogEvent.class);
        logs.add(
          new LevelAndMessage(logEvent.getLevel(), logEvent.getMessage().getFormattedMessage()));
        return null;
      }
Tests logging of large batch commands via Multi. Tests are fast, but uses a mini-cluster (to test
via "Multi" commands) so classified as MediumTests
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestMultiLogThreshold.java