Invocations of a method-ordered class template should run in parallel by default

[t-o-n-y-p]

Following the discussion here #5023

Steps to reproduce

1. Set up parallel test execution, for example, with 4 fixed threads
2. Write a method-ordered test class annotated with @TestMethodOrder(MethodOrderer.OrderAnnotation.class) and with order being assigned to its test methods
3. Declare this class a template and make a couple of invocations for it
4. Run the test class. Code example is provided below

junit.jupiter.execution.parallel.enabled=true
junit.jupiter.execution.parallel.mode.default=concurrent
junit.jupiter.execution.parallel.config.strategy=fixed
junit.jupiter.execution.parallel.config.fixed.parallelism=4

@ExtendWith(MethodOrderedClassTemplateExtension.class)
@ClassTemplate
@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
public class MethodOrderedClassTemplateTest {

  @Test
  @Order(0)
  void test1() throws InterruptedException {
    Thread.sleep(2000);
  }

  @Test
  @Order(1)
  void test2() throws InterruptedException {
    Thread.sleep(2000);
  }
}

@NullMarked
public class MethodOrderedClassTemplateExtension implements ClassTemplateInvocationContextProvider {
  @Override
  public boolean supportsClassTemplate(ExtensionContext context) {
    return true;
  }

  @Override
  public Stream<? extends ClassTemplateInvocationContext> provideClassTemplateInvocationContexts(ExtensionContext context) {
    return Stream.of(new ClassTemplateInvocationContext() {}, new ClassTemplateInvocationContext() {});
  }
}

Expected result

Invocations are being run in parallel while test method order is being respected within each invocation

Actual result

Invocations are being run sequentially

Context

• Used versions (Jupiter/Vintage/Platform): 6.0.0
• Build Tool/IDE: IntelliJ IDEA 2025.2.2

[prdoyle]

I have a situation where I'm running the exact same tests on three different databases using testcontainers. I'd like the three databases to run in parallel because they don't interfere with each other, but I'd like the methods to run one-at-a-time to keep the database load predictable so I don't start getting timeouts. I don't really want to write three classes to achieve this.