Overview

We should consider replacing our custom TestSourcesPlugin with Gradle's official support for Test Fixtures.

Rationale

• Currently all test code is visible in all other (downstream) projects, and that makes it too easy to introduce unnecessary coupling.
• For example, this made it more difficult to migrate to JUnit Jupiter.
• Having test fixture code in a dedicated source folder makes it readily apparent that the code is reused across the test suite.
• It will be much cleaner if projects explicitly declare that they rely on specific test fixtures of upstream projects.

Related Issues

• 23282

Comment From: marcphilipp

It will also make builds faster because test classes in downstream projects won't have to be recompiled and tests won't have to be executed if only a test class changes in an upstream project.

Comment From: sbrannen

Update: the work on this is essentially complete and can be viewed in the following feature branch.

https://github.com/sbrannen/spring-framework/commits/issues/gh-23550-test-fixtures

The only open issue is disabling the publication of *-test-fixtures artifacts. There is a built-in feature for that in Gradle 6.x, but we'll have to find a custom workaround for Gradle 5.6.x.