JUnit4 to JUnit5 migration

[UngureanuSerg]

Hi team,

A proposal to moving on after the adoption of java8+ is to start the migration from junit4 to jnuit5.

• JUnit 4 never advanced beyond Java 7, missing out on a lot of features from Java 8. JUnit 5 makes good use of the Java 8 features.
• A single jar library contains the entire framework. We need to import the whole library, even when we only require a particular feature. In JUnit 5, we get more granularity and can import only what's necessary.
• Only one test runner can execute tests at a time in JUnit 4 (e.g. @RunWith(Parameterized.class)
  or provide druid extension with the adoption of JUnit Platform). JUnit 5 allows multiple runners to work simultaneously.

As a strategy for the approach I would suggest to migrate one module at a time(it will be easier for the prs) and create tasks for the rest of the modules. As a starting point we can still depend on JUnit Vintage for backward compatibility with JUnit 4 but gradually moving to JUnit5.

I think all the point mentioned describes why it would be beneficial for apache druid as well as I would like to pick this issue if the rest of the community is interested.

[cryptoe]

@UngureanuSerg Thanks for starting this. Yes lets start the migration. Pretty excited 🚀 .
IMHO JUnit Vintage should be our last option. If we are able to move to the JUnit 5 using Unit Platform dependencies that would be even cooler.

[gianm]

@UngureanuSerg Thanks for starting this. Yes lets start the migration. Pretty excited 🚀 .
IMHO JUnit Vintage should be our last option. If we are able to move to the JUnit 5 using Unit Platform dependencies that would be event cooler.

I don't know the details, but if "JUnit Vintage" allows us to do a migration piece-by-piece instead of updating every test case at once, that sounds like a good thing. Updating every test case at once could potentially be a prohibitive amount of work for a single contributor.

[UngureanuSerg]

Hey Gian I didn't know that junit-vintage give this kind of capabilities but I will check it for sure

[dampcake]

In other projects I use junit-vintage to mix both JUnit5 and JUnit4 tests in the same suites. This allows for new tests or tests where you want to take advantage of the features to be converted while leaving all the existing tests on Junit4. Pretty much a best of both worlds scenario.

[kgyrtkirk]

there was a related PR to this: #16106 ;

I would like to leave a note here: to make sure that future PRs upgrading to junit5 should also configure openrewrite via rewrites.yml to ensure that no junit4 starts getting back into the upgraded testclasses (configuring that first and running the rewrite engine could jump-start the migration process as well)