endecode_test.c: Add tests for decoding with 0 selection

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from openssl#21519)

(cherry picked from commit 4c50610)
(cherry picked from commit 42f32b4)

test/endecode_test.c

@@ -158,6 +158,7 @@ static int test_encode_decode(const char *file, const int line,
     void *encoded = NULL;
     long encoded_len = 0;
     EVP_PKEY *pkey2 = NULL;
+    EVP_PKEY *pkey3 = NULL;
     void *encoded2 = NULL;
     long encoded2_len = 0;
     int ok = 0;
@@ -185,15 +186,25 @@ static int test_encode_decode(const char *file, const int line,
                                 output_type, output_structure,
                                 (flags & FLAG_DECODE_WITH_TYPE ? type : NULL),
                                 selection, pass))
+        || ((output_structure == NULL
+             || strcmp(output_structure, "type-specific") != 0)
+            && !TEST_true(decode_cb(file, line, (void **)&pkey3, encoded, encoded_len,
+                                    output_type, output_structure,
+                                    (flags & FLAG_DECODE_WITH_TYPE ? type : NULL),
+                                    0, pass)))
         || !TEST_true(encode_cb(file, line, &encoded2, &encoded2_len, pkey2, selection,
                                 output_type, output_structure, pass, pcipher)))
         goto end;
 
     if (selection == OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS) {
-        if (!TEST_int_eq(EVP_PKEY_parameters_eq(pkey, pkey2), 1))
+        if (!TEST_int_eq(EVP_PKEY_parameters_eq(pkey, pkey2), 1)
+            || (pkey3 != NULL
+                && !TEST_int_eq(EVP_PKEY_parameters_eq(pkey, pkey3), 1)))
             goto end;
     } else {
-        if (!TEST_int_eq(EVP_PKEY_eq(pkey, pkey2), 1))
+        if (!TEST_int_eq(EVP_PKEY_eq(pkey, pkey2), 1)
+            || (pkey3 != NULL
+                && !TEST_int_eq(EVP_PKEY_eq(pkey, pkey3), 1)))
             goto end;
     }
 
@@ -218,6 +229,7 @@ static int test_encode_decode(const char *file, const int line,
     OPENSSL_free(encoded);
     OPENSSL_free(encoded2);
     EVP_PKEY_free(pkey2);
+    EVP_PKEY_free(pkey3);
     return ok;
 }