Upgrade from Java 20 to 21 broke multi ParameterResolvers?

[thatsIch]

Hello community,

I use parameter resolvers to create preconditional objects for the tests like

class RandomIntegerParameterResolver implements ParameterResolver {
  @Override
  public boolean supportsParameter(ParameterContext parameterContext, ExtensionContext extensionContext) throws ParameterResolutionException {
      return parameterContext.getParameter().getType() == Integer.class;
  }

  @Override
  public Object resolveParameter(ParameterContext parameterContext, 
    ExtensionContext extensionContext) throws ParameterResolutionException {
      return ThreadLocalRandom.current().nextInt(0, 10);
  }
}

Sometimes it requires having multiple ParameterResolvers per test which can be injected through @ExtendWith:

@Test
@ExtendWith(RandomIntegerParameterResolver.class)
@ExtendWith(RandomDoubleParameterResolver.class)
void test(Integer i, Double d) {
    ...
}

But since Java 21 it broke for me in some projects.

Stacktrace

org.junit.jupiter.api.extension.ParameterResolutionException: Failed to resolve parameter [some.domain.Object arg1] in method [void some.domain.ObjectServiceIT.all(some.other.Object,some.domain.Object)]: class java.util.HashMap cannot be cast to class some.domain.Object (java.util.HashMap is in module java.base of loader 'bootstrap'; some.domain.Object is in unnamed module of loader 'app')
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
Caused by: java.lang.ClassCastException: class java.util.HashMap cannot be cast to class some.domain.Object (java.util.HashMap is in module java.base of loader 'bootstrap'; some.domain.Object is in unnamed module of loader 'app')
	at some.domain.ObjectParameterResolver.resolveParameter(ObjectParameterResolver.java:35)
	at some.domain.ObjectParameterResolver.resolveParameter(ObjectParameterResolver.java:14)
	... 2 more

where line 35 ist just the return like return ... which fails and line 14 is the class start.

Insights

• This worked without flaws with JUnit 5.10.1 (currently the latest version) running on Java 20 and Ubuntu 22.04.
• But when I upgraded to Java 21 it broke.
• Running the same test on Windows had the same result.
• Parallel execution does not matter when executing the tests through Maven.
• It does not fail when executing within Eclipse.
• Tests which only use one @ExtendWith do not fail

The above example sadly works so I have not found a good reproducer.
I try to identify in which layer the bug is.

Has somebody else encountered any problems like this?

I am currently trying to setup a reproducer for this problem, but I wanted to reach out here in parallel.

Thanks for reading!

[marcphilipp]

@thatsIch Any updates on the reproducer?

[thatsIch]

I had not the time to investigate further (felt like jumping into a rabbit hole). I got some free days before the holidays, so I will try to work from the other side and try to strip down the project to reduce the problem to a reproducer.

Thanks for the reminder.