Move org.springframework.boot.test.Assume to test-support

[sbrannen]

The new class org.springframework.boot.test.Assume refers to "JUnit" ambiguously.

Note, however, that org.junit.AssumptionViolatedException is specific to JUnit 4.

Thus, use of org.springframework.boot.test.Assume with JUnit Jupiter (or any other testing framework) would result in a failed test instead of an aborted test.

Since JUnit Jupiter uses org.opentest4j.TestAbortedException from the OTA for failed assumptions, I highly recommend that org.springframework.boot.test.Assume refer explicitly to JUnit 4 so as to avoid any confusion.

[philwebb]

See #9530. I'm tempted to move this to spring-boot-test-support and keep it internal to us.

[sbrannen]

If you don't plan to support it within the community, then I agree that keeping it internal would be the best choice.

[sbrannen]

Plus, if you were to migrate those tests to JUnit Jupiter and run them with the SpringExtension, it then becomes super easy to implement that support via a custom composed annotation that is meta-annotated with @EnabledIf( < SpEL expression > ) 😉