Add tests for enum helper

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index e9c74ca..67c0725 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -31,7 +31,9 @@
 int mbedtls_ssl_tls13_handshake_server_step( mbedtls_ssl_context *ssl )
 {
     ((void) ssl);
-    MBEDTLS_SSL_DEBUG_MSG( 2, ( "tls13 server state: %d", ssl->state ) );
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "tls13 server state: %s(%d)",
+                                mbedtls_ssl_states_str( ssl->state ),
+                                ssl->state ) );
 
     return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
 }