Add test for cache timeout getter

Signed-off-by: Pengyu Lv <pengyu.lv@arm.com>
diff --git a/tests/src/test_helpers/ssl_helpers.c b/tests/src/test_helpers/ssl_helpers.c
index 8e67352..5f203ab 100644
--- a/tests/src/test_helpers/ssl_helpers.c
+++ b/tests/src/test_helpers/ssl_helpers.c
@@ -93,6 +93,10 @@
     opts->cache = NULL;
     ASSERT_ALLOC(opts->cache, 1);
     mbedtls_ssl_cache_init(opts->cache);
+#if defined(MBEDTLS_HAVE_TIME)
+    TEST_EQUAL(mbedtls_ssl_cache_get_timeout(opts->cache),
+               MBEDTLS_SSL_CACHE_DEFAULT_TIMEOUT);
+#endif
 exit:
     return;
 #endif