Address the issue of replication throttle in Kafka broker implementat…

…ion (#594)

app/src/test/java/org/astraea/app/admin/ReplicationThrottlerTest.java

@@ -31,6 +31,12 @@
 
 public class ReplicationThrottlerTest extends RequireBrokerCluster {
 
+  /**
+   * There is a bug in the Kafka broker implementation. This will cause the replication throttle to
+   * act unstable at the beginning of replication. For more details, see <a
+   * href="https://github.com/apache/kafka/pull/12528">this</a>. This test attempt to ensure the
+   * throttle works smoothly. It is disabled since it won't pass until the bug is resolved.
+   */
   @EnabledIfEnvironmentVariable(named = "RunReplicationThrottler", matches = "^yes$")
   @Test
   void runReplicationThrottler() {