Update unit test doc

[res-life]

Closes #5467

Problem

case 1

cd spark-rapids
mvn test

The aggregator is a shading module, there are no classes under the aggregator/target/Sparkxxx/classes/ path.
So Maven tries to find the aggregator jar from local or remote repositories.

case 2

cd spark-rapids/tests
mvn test

By default, Maven tries to find an aggregator jar from local or remote repositories.

Changes

Due to the limitation of Maven, should first install the aggregator jar to the local repository.
Only need to update the doc.

Other context

The aggregator jar is not published to Maven Central.

Signed-off-by: Chong Gao res_life@163.com

[res-life]

build

[res-life]

Made an example, b module depends on a module.
mvn test -X shows the following:

[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ b ---
...
[DEBUG] test classpath classpath:
[DEBUG]   .../test-java-projects/b/target/test-classes
[DEBUG]   .../test-java-projects/b/target/classes
[DEBUG]   .../test-java-projects/a/target/classes

mvn test under the root directory, MVN adds the <dependency_module>/target/classes to the test classpath.
For the shading module, there are no target/classes directory.

[sameerz]

@tgravescs does this wording make sense?

Suggested change

	The `tests` module depends on the `aggregator` module which is shading the dependencies.
	Should first `mvn install` the aggregator jar to local Maven repository due to a limitation of the shading system.
	The steps to run the unit tests:
	The `tests` module depends on the `aggregator` module which shades dependencies. When running the
	tests, make sure to do an install via `mvn install` for the aggregator jar to the local maven
	repository.
	The steps to run the unit tests:

[tgravescs]

its close, we might add "When running the tests via 'mvn test', make...

[sameerz]

Updating the suggestion:

Suggested change

	The `tests` module depends on the `aggregator` module which is shading the dependencies.
	Should first `mvn install` the aggregator jar to local Maven repository due to a limitation of the shading system.
	The steps to run the unit tests:
	The `tests` module depends on the `aggregator` module which shades dependencies. When running the
	tests via `mvn test`, make sure to do an install via `mvn install` for the aggregator jar to the
	local maven repository.
	The steps to run the unit tests:

[res-life]

Done

[res-life]

build

[gerashegalov]

If we end up merely documenting the work around we should file another bug to actually make mvn test without workarounds possible

Ideally we should make test depend on dist, make sure that dist mimics the default maven phases correctly and customize test class path of the test module if necessary using additionalClassPathElements https://maven.apache.org/surefire/maven-surefire-plugin/examples/configuring-classpath.html

[res-life]

If we end up merely documenting the work around we should file another bug to actually make mvn test without workarounds possible

Ideally we should make test depend on dist, make sure that dist mimics the default maven phases correctly and customize test class path of the test module if necessary using additionalClassPathElements https://maven.apache.org/surefire/maven-surefire-plugin/examples/configuring-classpath.html

Thanks, @gerashegalov
The link you provided is helpful, in the link:

The Surefire plugin builds the test classpath in the following order:
  1. The test-classes directory
  2. The classes directory
  3. The project dependencies
  4. Additional classpath elements

If test depends on dist, the dependency type is: 3. The project dependencies

Already had an issue to try to depend on dist: #3932.
This issue was closed without a fix, please see details in the issue.

[gerashegalov]

Thanks for the reminder about #3192 @res-life.

In addition, another obstacle to making the test phase on the tests module working without a prior install is that the shade plugin only supports the package phase per https://maven.apache.org/plugins/maven-shade-plugin/

So there is no way to make the tests module run in the test phase using the aggregator jar produced only in the package phase