fix: poll bind via UDP before starting tests (#2475)

Potential fix for #2398: perhaps Bind is simply not fully
started and ready to respond to queries when we see
'Starting BIND' - potentially more reliable to perform
an actual request?

Author: raboof

actor-tests/src/test/scala/org/apache/pekko/io/dns/AsyncDnsResolverIntegrationSpec.scala

@@ -72,7 +72,7 @@ class AsyncDnsResolverIntegrationSpec
       system.log.info("Docker available. Running DNS tests")
     }
 
-    "resolve single A record" in {
+    "resolve a single A record" in {
       val name = "a-single.foo.test"
       val answer = resolve(name, DnsProtocol.Ip(ipv6 = false))
       withClue(answer) {

actor-tests/src/test/scala/org/apache/pekko/io/dns/DockerBindDnsService.scala

@@ -17,7 +17,6 @@ import scala.concurrent.duration._
 import scala.jdk.CollectionConverters._
 import scala.util.Try
 import scala.util.control.NonFatal
-
 import com.github.dockerjava.api.DockerClient
 import com.github.dockerjava.api.async.ResultCallback
 import com.github.dockerjava.api.command.CreateContainerCmd
@@ -26,10 +25,11 @@ import com.github.dockerjava.core.{ DefaultDockerClientConfig, DockerClientConfi
 import com.github.dockerjava.httpclient5.ApacheDockerHttpClient
 
 import org.apache.pekko
-import pekko.testkit.PekkoSpec
+import pekko.io.{ Dns, IO }
+import pekko.util.Timeout
 
+import pekko.testkit.PekkoSpec
 import org.scalatest.concurrent.Eventually
-
 import com.typesafe.config.Config
 
 abstract class DockerBindDnsService(config: Config) extends PekkoSpec(config) with Eventually {
@@ -122,6 +122,12 @@ abstract class DockerBindDnsService(config: Config) extends PekkoSpec(config) wi
 
       reader.toString should include("Starting BIND")
     }
+    eventually(timeout(25.seconds)) {
+      import pekko.pattern.ask
+      implicit val timeout: Timeout = 2.seconds
+      (IO(Dns) ? DnsProtocol.Resolve("a-single.foo.test", DnsProtocol.Ip(ipv6 = false))).mapTo[
+        DnsProtocol.Resolved].futureValue
+    }
   }
 
   def dumpNameserverLogs(): Unit = {