Migrate all tests to JUnit 5

[stefan-kolb]

1. Migrate all remaining tests
2. Remove obsolete Gradle dependencies & configurations

[Siedlerchr]

Our Importer/Exporter and a lot of our other tests rely on this feature:

Refs junit-team/junit5#1247
Currently planned for RC1

[LinusDietz]

Do we really need to migrate? The Junit5 vintage engine should run the old junit4 tests. I already removed the old dependencies at #3580

[stefan-kolb]

@LinusDietz Good question. If JUnit 4 support does not introduce additional dependencies, but is included in JUnit 5 per default, it is really just nice to have migration and not necessary. Could also be a nice beginners task then.

[tobiasdiez]

It is a separate dependency

jabref/build.gradle

Line 160 in 8265788

testRuntime 'org.junit.vintage:junit-vintage-engine:5.2.0-M1'

It would be nice to migrate all tests at some point to JUnit 5 but there is no real urgency in doing this. For now the only blocker is the temporary file / folder extension (although we could just copy the one provided in the junit sample rep), which, however, only affects a very small subset of our tests.

[Siedlerchr]

The TempoaryFolder extension will be published in the junit-pioneer project: junit-pioneer/junit-pioneer#39

[tobiasdiez]

The TempDir extension is now part of https://github.com/junit-pioneer/junit-pioneer and a test conversion to this extension can be found in 3c6bbd2 (sorry for pushing it directly onto the master).

[Siedlerchr]

Very good. So then we can go ahead converting the rest. I think this was the only issue left.

[tobiasdiez]

Thanks to @Metatronwings most of the tests are now converted. A few things remanin to be done (see #4260 (comment)), but require a new version of ArchUnit and/or JUnit. Thus, I put this issue on-hold for the momen.

[koppor]

Adressed by #5394.