fix javadsl awaitAssert in Typed, #25903

* returning null would result in retries until "timeout value is negative"
* use same implementation as in untyped
* real test

akka-actor-testkit-typed/src/main/scala/akka/actor/testkit/typed/internal/TestProbeImpl.scala

@@ -272,16 +272,22 @@ private[akka] final class TestProbeImpl[M](name: String, system: ActorSystem[_])
 
     @tailrec
     def poll(t: Duration): A = {
+      // cannot use null-ness of result as signal it failed
+      // because Java API and not wanting to return a value will be "return null"
+      var failed = false
       val result: A =
         try {
-          a
+          val aRes = a
+          failed = false
+          aRes
         } catch {
           case NonFatal(e) ⇒
+            failed = true
             if ((now + t) >= stop) throw e
             else null.asInstanceOf[A]
         }
 
-      if (result != null) result
+      if (!failed) result
       else {
         Thread.sleep(t.toMillis)
         poll((stop - now) min interval)

akka-actor-testkit-typed/src/main/scala/akka/actor/testkit/typed/javadsl/TestProbe.scala

@@ -269,7 +269,7 @@ abstract class TestProbe[M] {
     fishForMessage(max, "", fisher)
 
   /**
-   * Same as the other `fishForMessageJava` but includes the provided hint in all error messages
+   * Same as the other `fishForMessage` but includes the provided hint in all error messages
    */
   def fishForMessage(max: Duration, hint: String, fisher: java.util.function.Function[M, FishingOutcome]): java.util.List[M] =
     fishForMessage_internal(max.asScala, hint, fisher.apply).asJava

akka-actor-testkit-typed/src/test/java/akka/actor/testkit/typed/javadsl/TestProbeTest.java

@@ -5,6 +5,7 @@
 package akka.actor.testkit.typed.javadsl;
 
 import java.time.Duration;
+import java.util.Arrays;
 import java.util.List;
 
 import akka.actor.testkit.typed.scaladsl.TestProbeSpec;
@@ -54,4 +55,57 @@ public class TestProbeTest extends JUnitSuite {
     probe.receiveOne(Duration.ofMillis(100));
   }
 
+  @Test
+  public void testAwaitAssert() {
+    TestProbe<String> probe = TestProbe.create(testKit.system());
+    probe.awaitAssert(() -> {
+      // ... something ...
+      return null;
+    });
+    probe.awaitAssert(Duration.ofSeconds(3), () -> {
+      // ... something ...
+      return null;
+    });
+    String awaitAssertResult =
+      probe.awaitAssert(Duration.ofSeconds(3), Duration.ofMillis(100), () -> {
+        // ... something ...
+        return "some result";
+      });
+    assertEquals("some result", awaitAssertResult);
+  }
+
+  @Test
+  public void testExpectMessage() {
+    TestProbe<String> probe = TestProbe.create(testKit.system());
+    probe.getRef().tell("message");
+    String messageResult = probe.expectMessage("message");
+    probe.getRef().tell("message2");
+    String expectClassResult = probe.expectMessageClass(String.class);
+    probe.expectNoMessage();
+  }
+
+  @Test
+  public void testFish() {
+    TestProbe<String> probe = TestProbe.create(testKit.system());
+    probe.getRef().tell("one");
+    probe.getRef().tell("one");
+    probe.getRef().tell("two");
+    List<String> results = probe.fishForMessage(Duration.ofSeconds(3), "hint", message -> {
+      if (message.equals("one")) return FishingOutcomes.continueAndIgnore();
+      else if (message.equals("two")) return FishingOutcomes.complete();
+      else return FishingOutcomes.fail("error");
+    });
+    assertEquals(Arrays.asList("two"), results);
+  }
+
+  @Test
+  public void testWithin() {
+    TestProbe<String> probe = TestProbe.create(testKit.system());
+    String withinResult = probe.within(Duration.ofSeconds(3), () -> {
+      // ... something ...
+      return "result";
+    });
+    assertEquals("result", withinResult);
+  }
+
 }