Parallelize tests (except on CI)

[rschmitt]

This change enables JUnit 5's parallel mode. On my machine, this change causes ./mvnw to run in a third of the time (from 90 seconds to 30 seconds). Integration test time specifically has been reduced 80% (from 75 seconds to 15 seconds).

In order to prevent the introduction of reliability issues with CI builds, parallel execution is disabled in our maven.yml.

[ok2c]

@rschmitt Could you also mark AlpnTests @Isolated? I am getting test failures in that class when tests get executed in parallel.

I am also seeing lots of warnings

WARNING: Discovered 2 'junit-platform.properties' configuration files on the classpath (see below); only the first (*) will be used.
- file:/home/oleg/src/apache.org/httpcomponents/httpcore/httpcore5-testing/target/test-classes/junit-platform.properties (*)
- jar:file:/home/oleg/src/apache.org/httpcomponents/httpcore/httpcore5/target/httpcore5-5.5-alpha1-SNAPSHOT-tests.jar!/junit-platform.properties
Dec 21, 2025 9:46:24 AM org.junit.platform.launcher.core.LauncherConfigurationParameters loadClasspathResource
WARNING: Discovered 2 'junit-platform.properties' configuration files on the classpath (see below); only the first (*) will be used.
- file:/home/oleg/src/apache.org/httpcomponents/httpcore/httpcore5-testing/target/test-classes/junit-platform.properties (*)
- jar:file:/home/oleg/src/apache.org/httpcomponents/httpcore/httpcore5/target/httpcore5-5.5-alpha1-SNAPSHOT-tests.jar!/junit-platform.properties
Dec 21, 2025 9:46:25 AM org.junit.platform.launcher.core.LauncherConfigurationParameters loadClasspathResource
WARNING: Discovered 2 'junit-platform.properties' configuration files on the classpath (see below); only the first (*) will be used.
- file:/home/oleg/src/apache.org/httpcomponents/httpcore/httpcore5-testing/target/test-classes/junit-platform.properties (*)
- jar:file:/home/oleg/src/apache.org/httpcomponents/httpcore/httpcore5/target/httpcore5-5.5-alpha1-SNAPSHOT-tests.jar!/junit-platform.properties
Dec 21, 2025 9:46:25 AM org.junit.platform.launcher.core.LauncherConfigurationParameters loadClasspathResource
WARNING: Discovered 2 'junit-platform.properties' configuration files on the classpath (see below); only the first (*) will be used.
- file:/home/oleg/src/apache.org/httpcomponents/httpcore/httpcore5-testing/target/test-classes/junit-platform.properties (*)
...

Any chance those warnings could be avoided? They also seem to mess up SLF4J initialization

SLF4J: org.apache.hc.core5.testing.extension.classic.ClassicTestResources
SLF4J: The following set of substitute loggers may have been accessed
SLF4J: during the initialization phase. Logging calls during this
SLF4J: phase were not honored. However, subsequent logging calls to these
SLF4J: loggers will work as normally expected.
SLF4J: See also http://www.slf4j.org/codes.html#substituteLogger
SLF4J: org.apache.hc.core5.testing.extension.classic.ClassicTestResources
SLF4J: org.apache.hc.core5.testing.extension.classic.ClassicTestResources
SLF4J: org.apache.hc.core5.testing.extension.classic.ClassicTestResources
SLF4J: org.apache.hc.core5.testing.extension.classic.ClassicTestResources

[rschmitt]

Could you also mark AlpnTests @Isolated? I am getting test failures in that class when tests get executed in parallel.

There are three nested test classes in AlpnTests, two of which are disabled on macOS. I can mark these as @Isolated for now and come back to them later when I have better access to other test environments.

I am also seeing lots of warnings

Easy fix

They also seem to mess up SLF4J initialization

This appears benign but I think I can suppress it