8268023: Improve diagnostic for HandshakeFailureTest

Reviewed-by: chegar

src/java.net.http/share/classes/jdk/internal/net/http/Http2Connection.java

@@ -468,7 +468,9 @@ class Http2Connection  {
         Function<String, CompletableFuture<Void>> checkAlpnCF = (alpn) -> {
             CompletableFuture<Void> cf = new MinimalFuture<>();
             SSLEngine engine = aconn.getEngine();
-            assert Objects.equals(alpn, engine.getApplicationProtocol());
+            String engineAlpn = engine.getApplicationProtocol();
+            assert Objects.equals(alpn, engineAlpn)
+                    : "alpn: %s, engine: %s".formatted(alpn, engineAlpn);
 
             DEBUG_LOGGER.log("checkSSLConfig: alpn: %s", alpn );
 

test/jdk/java/net/httpclient/HandshakeFailureTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -266,7 +266,7 @@ public class HandshakeFailureTest {
         original.printStackTrace(System.out);
         throw new RuntimeException(
                 "Not found expected SSLHandshakeException in "
-                        + original);
+                        + original, original);
     }
 
     /** Common super type for PlainServer and SSLServer. */