fix t9400 test with JDK9+

[xuwei-k]

t9400.scala:2: error: class Deprecation needs to be abstract, since:
it has 2 unimplemented members.
/** As seen from class Deprecation, the missing signatures are as follows.
 *  For convenience, these are usable as stub implementations.
 */
  def forRemoval(): Boolean = ???
  def since(): String = ???

class Deprecation extends Deprecated {
      ^
one error found

[xuwei-k]

https://scala-ci.typesafe.com/job/scala-2.13.x-validate-main/4889/testReport/junit/scala.collection.immutable/ImmutableChampHashMapProperties/merged_right____select_left___is_the_same_as_right_concat_left/

#7254 😕 /cc @joshlemer

sbt.ForkMain$ForkError: java.lang.Exception: Falsified after 1 passed tests.
> ARG_0: HashMap( -> )
> ARG_1: HashMap( -> )
> ARG_1_ORIGINAL: HashMap( -> 㡑)
	at org.scalacheck.CustomScalaCheckRunner$$anon$2$$anon$3.<init>(CustomScalaCheckRunner.scala:126)
	at org.scalacheck.CustomScalaCheckRunner$$anon$2.executeInternal(CustomScalaCheckRunner.scala:115)
	at org.scalacheck.CustomScalaCheckRunner$$anon$2.$anonfun$execute$10(CustomScalaCheckRunner.scala:105)
	at org.scalacheck.CustomScalaCheckRunner$$anon$2.$anonfun$execute$10$adapted(CustomScalaCheckRunner.scala:104)
	at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:451)
	at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:449)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:898)
	at scala.collection.IterableOps$WithFilter.foreach(Iterable.scala:867)
	at org.scalacheck.CustomScalaCheckRunner$$anon$2.execute(CustomScalaCheckRunner.scala:104)
	at sbt.ForkMain$Run.lambda$runTest$1(ForkMain.java:304)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

[joshlemer]

Sorry! Looking into it

[joshlemer]

This should be fixed in #7289

As a side note, maybe the property tests should be pinned to a seed, so that they are deterministic?

[xuwei-k]

https://gist.github.com/non/aeef5824b3f681b9cfc141437b16b014

[xuwei-k]

rebased