Integrate JaCoCo "on-the-fly" in new URLClassLoader instances

[sorm...@gmail.com]

Hi JaCoCo team,

I'm writing a JUnit 5 support library that isolates main/test/others classes into dedicated class loaders. The first client of that library will be a Maven Plugin similar to Surefire. As I want to support "code coverage" early I'm thinking about ways how to enable this feature using JaCoCo.

At the moment, the new Maven Plugin executes tests "in-process" -- meaning the JaCoCo agent has already to be on the Maven boot class-path. Right?

Is there another way to get coverage data from a running process? Am I missing a/the point completely?

Cheers,
Christian

[Marc Hoffmann]

Hi Christian,

you might try offline instrumentation for the class files.

If you’re adding your own class loaders you might also consider doing on-the-fly instrumentation within your class loaders. See our API example “CoreTutorial”: https://www.jacoco.org/jacoco/trunk/doc/api.html

Regards,

-marc

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[sorm...@gmail.com]

On Friday, December 14, 2018 at 2:51:12 PM UTC+1, Marc R. Hoffmann wrote:
> Hi Christian,
>
>
> you might try offline instrumentation for the class files.
>
>
> If you’re adding your own class loaders you might also consider doing on-the-fly instrumentation within your class loaders. See our API example “CoreTutorial”: https://www.jacoco.org/jacoco/trunk/doc/api.html

Thanks for the quick reply, Marc!

And yes, that's exactly what I was looking for. Awesome.

Will report back when the integration is done. If you're interested in the progress, here is the tracking issue: https://github.com/sormuras/junit-platform-maven-plugin/issues/18

Cheers,
Christian

[Evgeny Mandrikov]

While you can do what Marc proposed,

recommended way of JaCoCo usage/integration - is agent,

mainly because of its simplicity in understanding by end-users,

especially compared to ClassLoaders.

Moreover

On Friday, December 14, 2018 at 2:16:06 PM UTC+1, sorm...@gmail.com wrote:

At the moment, the new Maven Plugin executes tests "in-process" --

IMO execution of tests inside of Maven process is a bad idea in general.

Not only agents can't be used, but also impossible to specify any other JVM options without affecting Maven - think about "-Xmx", "-D", etc.

So my advice will be to support out-of-Maven-process execution early. After that support of JaCoCo IMO will be much simpler to develop and maintain for you, and most importantly simpler to understand for end-users who are already familiar with usage of JaCoCo with maven-surefire-plugin.

[Marc Hoffmann]

I agree with Evgeny. There is another important requirement in many build setups:

You might want to use a different JDK for running your tests (e.g. when running your test suites against latest JDKs).

Cheers,

-marc

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[sorm...@gmail.com]

On Friday, December 14, 2018 at 6:01:03 PM UTC+1, Marc R. Hoffmann wrote:
> I agree with Evgeny. There is another important requirement in many build setups:
>
>
> You might want to use a different JDK for running your tests (e.g. when running your test suites against latest JDKs).
>

Thanks to both of you for mentioning those valid points. The new plugin will of course have a "fork option" that allows using jacoco et al like we are used to. Actually, the new plugin implementation started by calling the `junit-platform-console` program as an external process. I will re-introduce this mode later.

My question was related to the non-forked mode -- which will support jacoco soon with no user-interaction needed, because it is impossible.

[sorm...@gmail.com]

TWIMC, tracking issue: https://github.com/sormuras/junit-platform-maven-plugin/issues/20