Simplify the logic in a test

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index c069ee8..3aee2ba 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -1403,19 +1403,16 @@
             ret = mbedtls_ssl_encrypt_buf(&ssl, t_enc, &rec,
                                           mbedtls_test_rnd_std_rand, NULL);
 
-            if ((mode == 1 || mode == 2) && seen_success) {
-                TEST_ASSERT(ret == 0);
-            } else {
-                TEST_ASSERT(ret == 0 || ret == MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL);
-                if (ret == 0) {
-                    seen_success = 1;
-                }
-            }
-
-            if (ret != 0) {
+            if (ret == MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL) {
+                /* It's ok if the output buffer is too small. We do insist
+                 * on at least one mode succeeding; this is tracked by
+                 * seen_success. */
                 continue;
             }
 
+            TEST_EQUAL(ret, 0);
+            seen_success = 1;
+
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
             if (rec.cid_len != 0) {
                 /* DTLS 1.2 + CID hides the real content type and