tests: refactor schnorrsig module tagged hash tests

Add a comment for each tag.
Make character arrays static const unsigned char.
Update to use the sha256_tag_test_internal helper function.

Author: josibake

src/modules/schnorrsig/tests_impl.h

@@ -21,11 +21,12 @@ static void nonce_function_bip340_bitflip(unsigned char **args, size_t n_flip, s
 }
 
 static void run_nonce_function_bip340_tests(void) {
-    unsigned char tag[] = {'B', 'I', 'P', '0', '3', '4', '0', '/', 'n', 'o', 'n', 'c', 'e'};
-    unsigned char aux_tag[] = {'B', 'I', 'P', '0', '3', '4', '0', '/', 'a', 'u', 'x'};
+    /* "BIP0340/nonce" */
+    static const unsigned char tag[] = {'B', 'I', 'P', '0', '3', '4', '0', '/', 'n', 'o', 'n', 'c', 'e'};
+    /* "BIP0340/aux" */
+    static const unsigned char aux_tag[] = {'B', 'I', 'P', '0', '3', '4', '0', '/', 'a', 'u', 'x'};
     unsigned char algo[] = {'B', 'I', 'P', '0', '3', '4', '0', '/', 'n', 'o', 'n', 'c', 'e'};
     size_t algolen = sizeof(algo);
-    secp256k1_sha256 sha;
     secp256k1_sha256 sha_optimized;
     unsigned char nonce[32], nonce_z[32];
     unsigned char msg[32];
@@ -39,16 +40,15 @@ static void run_nonce_function_bip340_tests(void) {
     /* Check that hash initialized by
      * secp256k1_nonce_function_bip340_sha256_tagged has the expected
      * state. */
-    secp256k1_sha256_initialize_tagged(&sha, tag, sizeof(tag));
     secp256k1_nonce_function_bip340_sha256_tagged(&sha_optimized);
-    test_sha256_eq(&sha, &sha_optimized);
+    sha256_tag_test_internal(&sha_optimized, tag, sizeof(tag));
+
 
    /* Check that hash initialized by
     * secp256k1_nonce_function_bip340_sha256_tagged_aux has the expected
     * state. */
-    secp256k1_sha256_initialize_tagged(&sha, aux_tag, sizeof(aux_tag));
     secp256k1_nonce_function_bip340_sha256_tagged_aux(&sha_optimized);
-    test_sha256_eq(&sha, &sha_optimized);
+    sha256_tag_test_internal(&sha_optimized, aux_tag, sizeof(aux_tag));
 
     testrand256(msg);
     testrand256(key);