Alters POM to minimize test-compile dependencies

[smoyer64]

Overview

JUnit 5 has separated the public facing APIs from the runner, engines, launcher and console in an effort to keep test writers from using non-public classes when writing their tests. The existing Maven POM file adds dependencies these non-public classes to the test-compile scope which allows users to accidentally become dependent on these non-public classes. The test-compile dependency hierarchy in the existing POM is as follows:

This pull request alters the POM file so that the JUnit 5 classes exposed to the test writer are minimized. Since the runner and engine classes (and their dependencies) are required during test execution, these dependencies are instead added to the classpath when the maven-surefire-plugin is executed. After this change, the test-compile dependency hierarchy in the POM is as follows:

The results of running mvn clean test is unchanged, so the README file is still accurate.

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I hereby agree to the terms of the JUnit Contributor License Agreement.

[marcphilipp]

Why junit-platform-runner? If that were used it would need to be a test dependency, because it would be required by test-compile, wouldn't it?

[sbrannen]

I agree: the JUnitPlatform runner is only useful if a user can actually reference it from test classes.

[smoyer64]

You're right ... that dependency isn't needed. It seemed to be an artifact of some of the experiments I ran trying to use the JUnitPlatform runner without putting so many classes on the test-compile classpath. Those experiments ended up producing this issue in the JUnit 5 project: junit-team/junit5#498.

I'll alter this PR to match the users guide tomorrow when I get into work.

[marcphilipp]

Thanks for changing this! I've been meaning to do so myself a few times! 👍

[smoyer64]

I've eliminated the extra plugin dependency from this PR (junit-platform-runner).

[marcphilipp]

Thanks!