[MCOMPILER-478] testCompile with specific module-info.java partially copy target/classes to target/test-classes

**[Rocher Suchard](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=rocher.suchard)** opened **[MCOMPILER-478](https://issues.apache.org/jira/browse/MCOMPILER-478?redirect=false)** and commented

Hello,

I am trying to understand how I can fix this particular bug that occurs while compiling test sources with `src/test/java/module-info.java` (or `src/test/jpms/module-info.java` in my case because this would make Eclipse fails, due to having two module-info.java).

The `module-info` that I put in `src/test/jpms` is more or less the same as `{}src/main/jpms{`}, but with some test modules (like `{}org.opentest4j{`}, `{}org.junit.jupiter.api{`}, and `{}org.assertj.core{`}). This is pretty much what is explained here at the end of page: https://maven.apache.org/surefire/maven-surefire-plugin/examples/jpms.html#.

When I try to run tests, maven-surefire-plugin fails: the JVM is not happy about a package not found.

```java
1. Created at 2021-12-26T23:43:40.644
Corrupted STDOUT by directly writing to native stream in forked JVM 1. Stream 'Error occurred during initialization of boot layer'.
1. Created at 2021-12-26T23:43:40.647
Corrupted STDOUT by directly writing to native stream in forked JVM 1. Stream 'java.lang.module.FindException: Error reading module:'.
1. Created at 2021-12-26T23:43:40.647
Corrupted STDOUT by directly writing to native stream in forked JVM 1. Stream '...\target\test-classes'.
1. Created at 2021-12-26T23:43:40.648
Corrupted STDOUT by directly writing to native stream in forked JVM 1. Stream 'Caused by: java.lang.module.InvalidModuleDescriptorException:'.
1. Created at 2021-12-26T23:43:40.649
Corrupted STDOUT by directly writing to native stream in forked JVM 1. Stream 'Package org.acme.functions not found in module'.
```

At first, I thought it was something related to maven-surefire-plugin and I wanted to create a SUREFIRE JIRA issue, but I discovered that something - I presume maven-compiler-plugin - is copying used classes from `target/classes` to `target/test-classes` during test compilation.

In the case of my interface, it is not used and I presume the "something" that I speak about do partial copy of used files during compilation.

If we edit the src\main\java\org\acme\impl\AImpl.java to use the interface (should be commented in the attached ZIP):

```java
public class AImpl implements A {

@Override public void doSomethingCool() {
org.acme.functions.BooleanConsumer bc = v -> {};
throw new UnsupportedOperationException("no doing something cool");
}
}
```

The class file is copied and surefire does not fail.

The attached ZIP file exhibit the problem :

If we simply compile with tests: `{}mvn install{`}: `maven-surefire-plugin` will fails to execute test because of missing package. I could probably remove the offending package from test/module-info but I don't think I should tinker to much : the test/module-info should really "extends" the main/module-info and only add packages/modules.

If we skip test : `{}mvn install -DskipTests{`}: `maven-jar-plugin` will fails to execute to process due to a jar error {_}(jar: Package org.acme.functions missing from ModulePackages class file attribute{_}){_}.{_}

A solution to both issues would be to create dedicated tests project, with its own module-info.java and another module name (eg: org.acme.tests) but that would no longer be a (modular) white box testing.

**Note :** the attached project requires Maven 3.8.4 (there is a maven wrapper inside) and Java 17. I don't know if this fail with Java 11.

---

**Affects:** 3.8.1

**Attachments:**
- [surefire-empty-packages.zip](https://issues.apache.org/jira/secure/attachment/13037948/surefire-empty-packages.zip) (_15.46 kB_)