improve readability

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index fb2ae54..fc9b75c 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -1973,17 +1973,24 @@
      * Make sure both session structures are identical
      */
 #if defined(MBEDTLS_HAVE_TIME)
+    switch (tls_version) {
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3) && defined(MBEDTLS_SSL_SRV_C)
-    if (tls_version == MBEDTLS_SSL_VERSION_TLS1_3) {
-        TEST_ASSERT(original.ticket_creation_time == restored.ticket_creation_time);
-    }
+        case MBEDTLS_SSL_VERSION_TLS1_3:
+            TEST_ASSERT(original.ticket_creation_time == restored.ticket_creation_time);
+            break;
+#endif
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        case MBEDTLS_SSL_VERSION_TLS1_2:
+            TEST_ASSERT(original.start == restored.start);
+            break;
 #endif
 
-#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
-    if (tls_version == MBEDTLS_SSL_VERSION_TLS1_2) {
-        TEST_ASSERT(original.start == restored.start);
+        default:
+            /* should never happen */
+            TEST_ASSERT(0);
+            break;
     }
-#endif
+
 
 #endif
 
@@ -2246,20 +2253,28 @@
     ((void) tls_version);
     ((void) ticket_len);
     ((void) crt_file);
+
+    switch (tls_version) {
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
-    if (tls_version == MBEDTLS_SSL_VERSION_TLS1_3) {
-        TEST_ASSERT(mbedtls_test_ssl_tls13_populate_session(
-                        &session, 0, endpoint_type) == 0);
-    }
+        case MBEDTLS_SSL_VERSION_TLS1_3:
+            TEST_ASSERT(mbedtls_test_ssl_tls13_populate_session(
+                            &session, 0, endpoint_type) == 0);
+            break;
 #endif
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
-    if (tls_version == MBEDTLS_SSL_VERSION_TLS1_2) {
-        TEST_ASSERT(mbedtls_test_ssl_tls12_populate_session(
-                        &session, ticket_len, crt_file) == 0);
-    }
+        case MBEDTLS_SSL_VERSION_TLS1_2:
+            TEST_ASSERT(mbedtls_test_ssl_tls12_populate_session(
+                            &session, ticket_len, crt_file) == 0);
+            break;
 #endif
 
+        default:
+            /* should never happen */
+            TEST_ASSERT(0);
+            break;
+    }
+
     TEST_ASSERT(mbedtls_ssl_session_save(&session, NULL, 0, &good_len)
                 == MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL);
     TEST_CALLOC(good_buf, good_len);
@@ -2321,6 +2336,7 @@
         case MBEDTLS_SSL_VERSION_TLS1_2:
             TEST_ASSERT(mbedtls_test_ssl_tls12_populate_session(
                             &session, 0, NULL) == 0);
+
             break;
 #endif
         default: