Using StepVerifier in a parallel testing environment - project-reactor

Question

I am having some trouble when using StepVerifier's withVirtualTime and create methods in a parallel testing environment.
private static final Duration DELAY = Duration.ofSeconds(1);
public void testA() {
StepVerifier.withVirtualTime(() -> Mono.just(1).delayElement(DELAY))
.thenAwait(DELAY)
.expectNext(1)
.expectComplete()
.verify();
}
public void testB() {
StepVerifier.create(Mono.just(1).delayElement(DELAY))
.thenAwait(DELAY)
.expectNext(1)
.expectComplete()
.verify();
}
Maven Surefire plugin configuration:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.22.2</version>
<configuration>
<groups>unit</groups>
<includes>
<include>**/*Test.java</include>
</includes>
<parallel>methods</parallel>
<threadCount>2</threadCount>
<trimStackTrace>false</trimStackTrace>
</configuration>
</plugin>
These tests fail with the following exceptions (The full stack traces available on GitHub, please refer links below.):
[ERROR] testA(com.github.hisener.StepVerifierTest) Time elapsed: 0.04 s <<< FAILURE!
java.lang.NullPointerException: timedScheduler
at java.base/java.util.Objects.requireNonNull(Objects.java:246)
[ERROR] testB(com.github.hisener.StepVerifierTest) Time elapsed: 0.043 s <<< FAILURE!
reactor.core.Exceptions$ReactorRejectedExecutionException: Scheduler unavailable
at reactor.core.Exceptions.failWithRejected(Exceptions.java:249)
I don't think it's related to delayElements, for instance, one of the following tests uses timeout and they also fail:
public void testA() {
StepVerifier.withVirtualTime(() -> Mono.just(1)).expectNext(1).expectComplete().verify();
}
public void testB() {
StepVerifier.create(Mono.just(1).timeout(DELAY)).expectNext(1).expectComplete().verify();
}
I have tested on both TestNG and Junit 5, but no luck. The code is available on GitHub:
TestNG https://github.com/hisener/reactor-test-test
JUnit 5 https://github.com/hisener/reactor-test-test/tree/junit5

Answer 1

StepVerifier#withVirtualTime replaces ALL default Schedulers with the virtual time one, so it is not a good idea to use it in parallel