Tests within `inner class`es that are children of an `abstract class` are not executed despite `@Nested`

[SIMULATAN]

Expected

Tests declared within a @Nested inner class inheriting from their parent abstract class should run out of the box.

Actual

No tests are picked up.

Rationale

I want to test multiple strategies (MapperEngine). In order to verify feature parity, the tests are abstract functions.
To avoid boilerplate and group the tests, the strategy implementation verifications are inner classes of the abstract class.

Steps to reproduce

abstract class MapperEngineTest {
  abstract fun map()

  @Nested
  inner class Liquid : MapperEngineTest() {
    @Test
    // this test should run, but it doesn't
    override fun map() { ... }
  }

  @Nested
  inner class Replace {
    @Test
    // doesn't run either (this time without inheriting the abstract class)
    fun map() { ... }
  }
}

Context

• Used versions: JUnit 5.10.2
• Build Tool/IDE: Gradle 8.10.2, IntelliJ 2024.3 RC

[marcphilipp]

For @Nested on inner classes to work, JUnit needs to be able to create an instance of the enclosing class. Since it's abstract that doesn't work here. Instead of using @Nested (which requires inner classes) you should use regular "static" classes:

abstract class MapperEngineTest {
    abstract fun map()

    class Liquid : MapperEngineTest() {
        @Test
        override fun map() { fail("boom") }
    }

    class Replace {
        @Test
        fun map() { fail("boom") }
    }
}

[marcphilipp]

I've added this issue to #242 which will introduce an error reporting mechanism that should be triggered if such a @Nested annotation is found on a inner class of an abstract class so you'd notice what's wrong sooner.

[SIMULATAN]

@marcphilipp thank you for the quick help, that works as expected indeed!
The error report mechanism would be awesome to avoid such issues in the future.