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Posted to notifications@pekko.apache.org by "ccerbusca (via GitHub)" <gi...@apache.org> on 2024/02/22 15:23:26 UTC
[I] NullPointerException when overriding testKit from ScalaTestWithActorTestKit [incubator-pekko]
ccerbusca opened a new issue, #1140:
URL: https://github.com/apache/incubator-pekko/issues/1140
While migrating a project to Pekko, I noticed that some of the tests started failing with `NullPointerException`s.
On further investigation, it was because I was overriding the TestKit inside those tests.
Here's a simple reproducer:
```scala
import org.apache.pekko.actor.testkit.typed.scaladsl.{ActorTestKit, ScalaTestWithActorTestKit}
import org.scalatest.funsuite.AnyFunSuiteLike
class Test extends ScalaTestWithActorTestKit with AnyFunSuiteLike {
override val testKit = ActorTestKit()
test("test") {
assert(true)
}
}
```
I think the issue seems to be this line, where the `val` is not lazy, leading to a NullPointerException.
https://github.com/apache/incubator-pekko/blob/28314e679885519f6458ebf10f9a181d5299c83a/actor-testkit-typed/src/main/scala/org/apache/pekko/actor/testkit/typed/scaladsl/ScalaTestWithActorTestKit.scala#L94
I understand that in this case I should have passed the `TestKit` to the `ScalaTestWithActorTestKit` constructor (which I do now), but having the ability to override `testKit`, makes it a possible usage for other people too.
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Re: [I] NullPointerException when overriding testKit from ScalaTestWithActorTestKit [incubator-pekko]
Posted by "jxnu-liguobin (via GitHub)" <gi...@apache.org>.
jxnu-liguobin commented on issue #1140:
URL: https://github.com/apache/incubator-pekko/issues/1140#issuecomment-1962247804
Can we add documentation to explain it？
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Re: [I] NullPointerException when overriding testKit from ScalaTestWithActorTestKit [incubator-pekko]
Posted by "mdedetrich (via GitHub)" <gi...@apache.org>.
mdedetrich commented on issue #1140:
URL: https://github.com/apache/incubator-pekko/issues/1140#issuecomment-1959726961
I don't think this is generally solvable due to how trait initialization works in Scala 2, long story short trait composition in Scala 2 is not commutative which means that the order of when you mix in traits can effect initialization which can lead to `NullPointerException` in cases like this.
The solution to this problem is to use `lazy val`/`def`. Also afaik this is not an issue in Scala 3 where the compiler will re-order the fields in traits to make sure its initialized correctly.
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Re: [I] NullPointerException when overriding testKit from ScalaTestWithActorTestKit [incubator-pekko]
Posted by "mdedetrich (via GitHub)" <gi...@apache.org>.
mdedetrich commented on issue #1140:
URL: https://github.com/apache/incubator-pekko/issues/1140#issuecomment-1962277728
> Can we add documentation to explain it？Although this is an initialization pit.
Sure, although I wouldn't spend too much time on it because as said previously it really has nothing specifically to do with Pekko.
I would propose adding a single line in the docs briefly explaining the problem containing a link to an official Scala 2 source explaining this.
I will also remove the bug label for this reason.
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