Suspecting a bug in org.scalatest.concurrent.AsynchronousAssertions.Waiter. The code below fails pretty reliably. There seems to be a window of vulnerability in awaitImpl(): if the last (or last few) dismiss() calls happen after the dismissals count test at the top of the while() loop, but the associated notifyAll() invocations happen before the…

WaiterSpec.scala

package scratch

// scalatest 2.0.M8

import org.scalatest.WordSpec
import org.scalatest.matchers.ShouldMatchers
import org.scalatest.concurrent.AsyncAssertions
import org.scalatest.time.{ Span, Millis }

class WaiterSpec extends WordSpec with ShouldMatchers with AsyncAssertions {
  "A Waiter instance" should {
    "not break when beaten on" in {
      val n = 100000
      val w = new Waiter
      new Thread(new Runnable {
        override def run(): Unit = {
          var i = 0
          while (i < n) { w.dismiss(); i += 1 }
          println(s"i=$i")
        }
      }).start
      w.await(timeout(Span(2000, Millis)), dismissals(n))
    }
  }
}

OK, pull request made. Happy to iterate if necessary.