How to test messages logged by the app in Mule 4 EE

Question

For a Mule 4 EE app, I am writing integration tests using JUnit4 and Rest Assured. In a test I am trying to verify that certain messages are logged by the app. How can I do that?

I wrote a customer appender and attached it to the root logger, but it is not getting any messages. Update - that's not working because the Mule runtime is running in a separate process and the test is not able to tap into the runtime's logger.

static class TestAppender extends AppenderSkeleton {
    public List<org.apache.log4j.spi.LoggingEvent> events =
        new ArrayList<org.apache.log4j.spi.LoggingEvent>();

    public void close() {}

    public void clearLog() {
      events.clear();
    }

    public boolean requiresLayout() {
      return false;
    }

    @Override
    protected void append(LoggingEvent event) {
      events.add(event);
    }
  }

and the test

// is not working
@Test
public void test_log_msg() throws Exception {
 TestAppender testAppender = new TestAppender();
 Logger.getRootLogger().addAppender(testAppender);
 // perform some action that causes logging
 assertEquals(testAppender.events.size(), 1);
}

Any help will be greatly appreciated.

Specifically, I am trying to verify that caching is working for my API. I was going to do that by verifying the messages that I am logging in the app when the caching happens. If there is a more elegant approach to doing it, please let me know.

Answer 1

I don't think this is a good test design. Logging is not meant for unit testing checks. The test will be easy to break. Also technically the implementation in Mule 4 as you mentioned is not easy or possible to capture in that way. Add to it that currently Mule 4 only supports MUnit, not JUnit.

I would recommend to go back a step and think what your test should be really validating, which is the caching and not the logging. Try to implement it using MUnit if possible.