[fix][test] Fix flaky RateLimiterTest.testDispatchRate (#25846)

Author: lhotari

pulsar-common/src/test/java/org/apache/pulsar/common/util/RateLimiterTest.java

@@ -26,6 +26,7 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Supplier;
 import lombok.Cleanup;
+import org.awaitility.Awaitility;
 import org.testng.annotations.Test;
 
 public class RateLimiterTest {
@@ -201,13 +202,13 @@ public void testDispatchRate() throws Exception {
         rate.tryAcquire(100);
         assertEquals(rate.getAvailablePermits(), 0);
 
-        Thread.sleep(rateTimeMSec * 2);
-        // check after two rate-time: acquiredPermits is 100
-        assertEquals(rate.getAvailablePermits(), 0);
-
-        Thread.sleep(rateTimeMSec);
-        // check after three rate-time: acquiredPermits is 0
-        assertTrue(rate.getAvailablePermits() > 0);
+        // Each scheduled renew releases `permits` (100) from acquiredPermits (which starts at 300).
+        // Wait until the renew task has run enough times to make permits available again. Polling
+        // avoids flakiness caused by scheduler jitter under CI load that delays fixed-rate ticks.
+        Awaitility.await()
+                .atMost(rateTimeMSec * 10, TimeUnit.MILLISECONDS)
+                .pollInterval(100, TimeUnit.MILLISECONDS)
+                .until(() -> rate.getAvailablePermits() > 0);
 
         rate.close();
     }