Improve a test assertion

That way if it ever fails it will print the values.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 20e0995..cc47eb5 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -5092,7 +5092,7 @@
 
     /* Send the crafted message */
     ret = mbedtls_test_mock_tcp_send_b(&client.socket, data->x, data->len);
-    TEST_ASSERT(ret >= 0 && (size_t) ret == data->len);
+    TEST_EQUAL(ret, (int) data->len);
 
     /* Have the server process it.
      * Need the loop because a server that support 1.3 and 1.2