How to capture log output from Flux in these unit tests?

I am checking out the example code in this project https://github.com/balamaci/reactor-core-playground#simple-operators

Here is a typical function in the source code

@Test
public void delayElements() {
CountDownLatch latch = new CountDownLatch(1);
log.info("Starting");
Flux.range(0, 5)
.doOnNext(val -> log.info("Emitted {}", val))
.delayElements(Duration.of(2, ChronoUnit.SECONDS))
.subscribe(
tick -> log.info("Tick {}", tick),
(ex) -> log.info("Error emitted"),
() -> {
log.info("Completed");
latch.countDown();
});
Helpers.wait(latch);
}

I want to be able to see the log output like Error emitted.

However if i run mvn test I cannot see any stdout output at all.

I have tried to enable log capture in the surefire plugin but it also does not achieve anything

+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-surefire-plugin</artifactId>
+          <configuration>
+            <redirectTestOutputToFile>true</redirectTestOutputToFile>
+          </configuration>
+        </plugin>

There is a property file in the resource

org.slf4j.simpleLogger.logFile=System.out
org.slf4j.simpleLogger.defaultLogLevel=info
org.slf4j.simpleLogger.showDateTime=true
org.slf4j.simpleLogger.dateTimeFormat=HH:mm:ss:SSS
org.slf4j.simpleLogger.showThreadName=true
org.slf4j.simpleLogger.showShortLogName=true 

But the output is still

$ mvn test
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------< com.balamaci:reactor-playground >-------------------
[INFO] Building Reactor-Core Playground 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ reactor-playground ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/antkong/experiments/flux/reactor-core-playground/src/main/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ reactor-playground ---
[INFO] No sources to compile
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ reactor-playground ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 2 resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ reactor-playground ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:3.0.0-M5:test (default-test) @ reactor-playground ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.657 s
[INFO] Finished at: 2020-08-21T18:27:58+10:00
[INFO] ------------------------------------------------------------------------

In this case, how can I capture the log output?

It seems like you don’t have any logger implementation on classpath. Try adding the following:

<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
</dependency>

and create resources/logback.xml

<configuration>
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<!-- encoders are assigned the type
ch.qos.logback.classic.encoder.PatternLayoutEncoder by default -->
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<root level="info" additivity="false">
<appender-ref ref="STDOUT"/>
</root>
</configuration>

The issue here seems to be lack of Test word in class names, so they are not ran at all. Commands like mvn test -Dtest=Part02SimpleOperators, where you provide a name, work just fine.