If I'm making an abstract base class for tests that need a testcontainers db connection (in Micronaut Test), is there some kind of generic test type I can use, and then just use whichever of the styles in the actual tests inherited from it?

What you need is a kind of uber style.

disclaimer first, we don’t use kotest testcontainers library because we started with testcontainers before I found about the library (and you know, as long as it works - and it is not too ugly) and we use spring boot, but we did something like

class ProjectConfig : AbstractProjectConfig() {
  override fun listeners() = listOf(PostgresListener, SpringListener, object : TestListener {
    override suspend fun afterTest(testCase: TestCase, result: TestResult) {
      clearAllMocks()
    }
  })
}

object PostgresListener : ProjectListener {
  private val withNetworkAliases = PostgreSQLContainerProvider().newInstance("10")
    .withNetwork(Network.SHARED)
    .withNetworkAliases("db")

  override suspend fun beforeProject() {
    withNetworkAliases.start()
    System.setProperty("spring.datasource.url", "jdbc:postgresql://${withNetworkAliases.connectionString()}")
    System.setProperty("spring.datasource.username", withNetworkAliases.getUsername())
    System.setProperty("spring.datasource.password", withNetworkAliases.getPassword())
    System.setProperty("spring.flyway.schemas", withNetworkAliases.getDatabaseName())
  }

  override suspend fun afterProject() {
    withNetworkAliases.stop() //probably not needed because of ryuk
  }

  private fun JdbcDatabaseContainer<*>.connectionString() = "${getHost()}:${getFirstMappedPort()}/${getDatabaseName()}"

  override val name = "PostgresListener"
}

then db tests can be regular

SpringBootTest

(or test slice if only the db is needed) since the configuration properties are set. I don’t know micronaut (it might or might not be explored in the service we need to implement), but something like this might work for you as well

You're probably right @thanksforallthefish, in this case a listener could do the trick. But we find ourselves injecting a bunch of deps on the test level for, say, integration testing, that might not be needed in other tests. There is a way to register listeners on the class level, but having a base class might be a bit clearer...