Support Kotlin top level functions as test methods

[mmerdes]

In Kotlin, functions are first class citizens and do not need the context of a class definition.
Idiomatic Kotlin often tries to avoid as much code as possible.
The current implementation of JUnit Jupiter does not allow to execute such top level functions as tests.
As Kotlin top level functions are compiled to static JVM methods with a predictable class name and an annotation identifying the generated class as a Kotlin class, it should be possible to add such support.

Complete example of tests without a class definition:

import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test


@Test
fun failure() = assertTrue(false)

@Test
fun success() = assertTrue(true)

Careful thought about possible limitations to life-cycle methods might be in order.

Deliverables

• add ability to execute Kotlin top level functions as tests

[mmerdes]

Thanks to @jlink for alerting me to the possibility to identify compiled Kotlin files by annotation means.

[marcphilipp]

Team decision: @mmerdes will explore and potentially spike how this could be implemented.

Known caveats: No lifecycle methods (maybe @BeforeAll/@AfterAll), extensions that require test instances would throw exceptions

[jlink]

Mind that IDE's will have to adapt to show top-level functions as testable methods.

[mmerdes]

Well, they should show anything meta-annotated with @Testable as executable anyway, shouldn't they?

[jlink]

But they don't. In many places. Other example:

obect Tests {
    @Test fun myTest() {}
}

I've already submitted a few bugs in that regard, e.g. https://youtrack.jetbrains.com/issue/KT-49491
You should open one for top-level functions as well.

I haven't looked at Eclipse's JUnit platform support in years. It may be better - or it may be worse.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Given the limited bandwidth of the team, it will be automatically closed if no further activity occurs. Thank you for your contribution.

[mmerdes]

still interested in this and hope to give it a try some time in 2023...