disableConsoleOutput() in a @SpringBootTest: "Attempted to append to non started appender"

[DamianFekete]

Describe the bug
A warning is printed to the console if disableConsoleOutput() is called in a @SpringBootTest test.

15:06:51,602 |-WARN in ch.qos.logback.core.ConsoleAppender[CONSOLE] - Attempted to append to non started appender [CONSOLE].

I have added it as bug, but only because I haven't seen any discussion on this topic.
I am not sure what the solution would be (maybe replacing the listener instead of closing it, I don't know if this is even possible).

The warning is added by ch.qos.logback.core.UnsynchronizedAppenderBase.

The warning is printed here (because a listener is present in BasicStatusManager#fireStatusAddEvent, listener added by Spring Boot):

The StatusListener is added here:

https://github.com/spring-projects/spring-boot/blob/9ab0d28cebb925661c0c1b7e2198cfc31d2d8ef3/core/spring-boot/src/main/java/org/springframework/boot/logging/logback/SystemStatusListener.java#L89

To Reproduce
Run the test test while keeping the line removeSystemListener(); commented.
If you enable the call removeSystemListener(); the warning goes away.

@SpringBootTest
public class TestCaptor {

    private static final Logger log = LoggerFactory.getLogger(TestCaptor.class);
    private LogCaptor logCaptor;

    @BeforeEach
    void setUp() {
        logCaptor = LogCaptor.forClass(TestCaptor.class);
        logCaptor.disableConsoleOutput();
//        removeSystemListener();
    }

    @AfterEach
    void tearDown() {
        logCaptor.close();
    }

    @Test
    void test() {
        log.info("Test abc");
    }

    private void removeSystemListener() {
        var logger = ((ch.qos.logback.classic.Logger) LoggerFactory.getLogger(this.getClass()));
        var sm = logger.getLoggerContext().getStatusManager();
        var listeners = sm.getCopyOfStatusListenerList();
        for (var listener : listeners) {
            if (listener instanceof OnConsoleStatusListener) {
                sm.remove(listener);
            }
        }
    }
}

Expected behavior
No warning should be visible on the console.

Environmental Data:

• Java Version 21
• Maven Version 3.9.12
• OS Linux
• Spring Boot 4.0.1

[Hakky54]

Hi @DamianFekete good catch and thank you for sharing this issue. I was able to reproduce on my side. These warnings should not happen, but it seems like it is occuring because the way how the console logs are being disabled. I have made a fix to resolve it. I tested it on my side and it works. I will create a new release this evening.

[Hakky54]

The fix is now available in version 2.12.2 Can you try on your side and share your results?

[DamianFekete]

Hi @Hakky54, I've tested and everything looks good, thank you very much for your very fast response!

Have a great weekend!

---

One additional remark, as I had this discussion at work just this week:

You're declaring static fields using UPPER_CASE, even though they are not constants.

log-captor/src/main/java/nl/altindag/log/LogCaptor.java

Line 49 in 8e9384f

private static final Map<String, Optional<Appender<ILoggingEvent>>> CONSOLE_APPENDER_CONTAINER = new HashMap<>();

I would like to know the reasoning behind it. Do you use a specific style guide?

For example, from https://google.github.io/styleguide/javaguide.html#s5.2.4-constant-names:

But what is a constant, exactly?

Constants are static final fields whose contents are deeply immutable and whose methods have no detectable side effects. Examples include primitives, strings, immutable value classes, and anything set to null. If any of the instance's observable state can change, it is not a constant. Merely intending to never mutate the object is not enough.

[Hakky54]

Great that is works now!

One additional remark, as I had this discussion at work just this week:
You're declaring static fields using UPPER_CASE, even though they are not constants.

You are right, I have the habbit of naming fields upper snake case when it is static and final. But having something upper snake case means a constant and in this case that field is definitely not a constant. I have adjusted it here, thank you for noticing and sharing it!

If you find anything else in this project or my other projects, feel free to submit a pull request 😄