How to intercept SLF4J (with logback) logging via a JUnit test?

Question

Is it possible to somehow intercept the logging (SLF4J + logback) and get an InputStream (or something else that is readable) via a JUnit test case...?

Answer 1

With JUnit5 + AssertJ

private ListAppender logWatcher;

@BeforeEach
void setup() {
  this.logWatcher = new ListAppender<>();
  this.logWatcher.start();
  ((Logger) LoggerFactory.getLogger(MyClass.class)).addAppender(this.logWatcher);
}


@Test
void myMethod_logs2Messages() {

  ...
  int logSize = logWatcher.list.size();
  assertThat(logWatcher.list.get(logSize - 2).getFormattedMessage()).contains("EXPECTED MSG 1");
  assertThat(logWatcher.list.get(logSize - 1).getFormattedMessage()).contains("EXPECTED MSG 2");
}

---

credits to: @davidxxx's answer. See it for import ch.qos.logback... details: https://stackoverflow.com/a/52229629/601844