Investigate JUnit 5

[philwebb]

JUnit 5 looks like it might be a very awkward upgrade for both our users and Spring Boot itself. We'll need to come up with a plan going forward for how people should upgrade.

Of particular concern:

• You can't just run JUnit 4 tests with JUnit 5 😢
• There are new @Test annotations and expectedException has been dropped
• There is no @Rule annotation (this will break a lot of our tests and we'll need to offer alternatives to the rules we offer)

We might be able to offer JUnit 5 alongside JUnit 4 for a while (possibly a long while) so that people can use both.

I imagine probably going to frustrate a lot of users given that mostly their own test code has very little direct contact with the JUnit API. Mostly people use @Test, @Before/@After, perhaps a few @Rule annotations and some Assert calls.

Related issue junit-team/junit-framework#169

[philwebb]

/cc @sbrannen

[marcphilipp]

Regarding the first bullet point: You can run JUnit 4 tests with the new JUnit Platform. You just have to add junit-vintage-engine to the classpath.

Please note that JUnit 5 is not final yet. We've merely shipped M1. As such, we are still working on providing migration patterns from JUnit 4 to JUnit 5. So let's keep in touch! :)

[philwebb]

Thanks @marcphilipp!

[sdeleuze]

JUnit 5 support would be very useful as part of the general Spring Boot + Kotlin improvements discussed in #5537.

Using JUnit 4 in Kotlin is almost ok except for one major pain point: @BeforeClass and @AfterClass have to be static methods, and Kotlin does have that. There is an ugly workaround using companion object but this is not something we should promote IMO. Even in Java this limitation (that TestNG does not have) can be annoying, even there is less impact than in Kotlin.

The good news is that JUnit 5 M4 is likely to support non-static @BeforeAll and @AfterAll methods (the related issue is junit-team/junit-framework#419). If that happens, it would make JUnit 5 a very nice fit for testing Spring Boot + Kotlin applications.

cc @sbrannen

[jchesterpivotal]

Speaking only for myself, the @DisplayName and @Nested annotations introduced by Jupiter could allow more BDD-ish style testing with JUnit. I'd be in favour of some kind of support showing up in the 2.x series.

[driverpt]

@philwebb , i believe that it's possible to run JUnit4 Tests with JUnit5, from what i understand, you just need to add the junit-vintage-engine artifact

Link

I think that we should integrate JUnit5 as standard in spring-boot-starter-test and add a spring-boot-starter-test-junit4-compat artifact to support Legacy JUnit4 stuff. And for those who are more conservative, just have a spring-boot-starter-test-junit4 just with JUnit 4

[pvorb]

JUnit 5 has been released!

Would it make sense to work on support for JUnit 5 for Spring Boot 2?

[wilkinsona]

Thanks to Spring Framework's test framework, we don't really need to do anything in Boot to support JUnit 5. We already have a sample showing how to use the two together.

[snicoll]

And we have dependency management for it now (see #10240). I suspect we'll need to refine this a bit more though.

[pvorb]

I didn't know it's already usable. So much the better!