comments.

server/src/main/java/org/elasticsearch/common/util/concurrent/EsExecutors.java

@@ -268,7 +268,9 @@ public static String threadName(final String nodeName, final String namePrefix)
 
     // to be used in assertions only.
     public static boolean differentExecutors(Thread thread1, Thread thread2) {
-        assert thread1 != thread2 : "only call for different threads";
+        // this should only be used to validate thread interactions, like not waiting for a future completed on the same
+        // executor, hence calling it with the same thread indicates a bug in the assertion using this.
+        assert thread1 != thread2 : "only call this for different threads";
         String thread1Name = executorName(thread1);
         String thread2Name = executorName(thread2);
         return thread1Name == null || thread2Name == null || thread1Name.equals(thread2Name) == false;
@@ -277,6 +279,7 @@ public static boolean differentExecutors(Thread thread1, Thread thread2) {
     // visible for tests
     static String executorName(Thread thread) {
         String name = thread.getName();
+        // subtract 2 to avoid the `]` of the thread number part.
         int executorNameEnd = name.lastIndexOf(']', name.length() - 2);
         int executorNameStart = name.lastIndexOf('[', executorNameEnd);
         if (executorNameStart == -1 || executorNameEnd - executorNameStart <= 1) {