Auto-label containers with test class and field in @Testcontainers extension

[lekhrocks]

Closes #11919

Before starting a container via @Testcontainers, the JUnit extension now sets two identifying labels on the container:

testcontainers/test-class  -> "com.example.MyPostgresTest"
testcontainers/test-field  -> "postgresContainer"

This lets users identify which container belongs to which test at a glance:

docker ps --filter label=testcontainers/test-class=com.example.MyPostgresTest

And trace CI failures back to the owning test from container metadata.

[eddumelendez]

Can we please discuss the ideas before raising a PR?

[lekhrocks]

Can we please discuss the ideas before raising a PR?

@eddumelendez

Makes sense! I should have started with a discussion first. I've opened one here: #11919. Happy to iterate on the approach based on maintainer feedback before reopening the PR.

[eddumelendez]

Thanks for your contribution. Two things:

1. Testcontainers uses org.testcontainers prefix for labels and those are immutable. I think this can be addressed.
2. There will be an inconsistency about how containers are created using JUnit integration.

I think this is useful information, in the past thought about it as well but didn't dig deeper into the second item. I also thought about an specific section in the JUnit report.

For now, I would avoid having different ways to create a container.

[lekhrocks]

Thanks for your contribution. Two things:

1. Testcontainers uses org.testcontainers prefix for labels and those are immutable. I think this can be addressed.
2. There will be an inconsistency about how containers are created using JUnit integration.

I think this is useful information, in the past thought about it as well but didn't dig deeper into the second item. I also thought about an specific section in the JUnit report.

For now, I would avoid having different ways to create a container.

@eddumelendez
Thanks for the thoughtful review, both points make sense.

1. The label prefix is easy to fix - org.testcontainers is the right namespace.
2. The inconsistency between container creation paths is a real problem I hadn't fully accounted for. Labels on containers started via @Testcontainers but not on manually created containers would be confusing.

I think a better approach would be something in the JUnit report layer, a test execution listener that captures container IDs and maps them to test class/method in the report output. That way it works uniformly regardless of how containers are created. I'd be happy to explore that direction in a future contribution.

Thanks again for the feedback.