tests: Fix tests by adding a global copy of secp256k1_context_static

Author: real-or-random

src/modules/extrakeys/tests_impl.h

@@ -336,7 +336,6 @@ void test_keypair(void) {
     secp256k1_xonly_pubkey xonly_pk, xonly_pk_tmp;
     int pk_parity, pk_parity_tmp;
     int ecount;
-    secp256k1_context *sttc = secp256k1_context_clone(secp256k1_context_static);
 
     set_counting_callbacks(ctx, &ecount);
     set_counting_callbacks(sttc, &ecount);

src/modules/recovery/tests_impl.h

@@ -30,7 +30,6 @@ static int recovery_test_nonce_function(unsigned char *nonce32, const unsigned c
 
 void test_ecdsa_recovery_api(void) {
     /* Setup contexts that just count errors */
-    secp256k1_context *sttc = secp256k1_context_clone(secp256k1_context_static);
     secp256k1_pubkey pubkey;
     secp256k1_pubkey recpubkey;
     secp256k1_ecdsa_signature normal_sig;

src/modules/schnorrsig/tests_impl.h

@@ -128,8 +128,7 @@ void test_schnorrsig_api(void) {
     secp256k1_schnorrsig_extraparams invalid_extraparams = {{ 0 }, NULL, NULL};
 
     /** setup **/
-    secp256k1_context *sttc = secp256k1_context_clone(secp256k1_context_static);
-    int ecount;
+    int ecount = 0;
 
     secp256k1_context_set_error_callback(ctx, counting_illegal_callback_fn, &ecount);
     secp256k1_context_set_illegal_callback(ctx, counting_illegal_callback_fn, &ecount);

src/tests.c

@@ -29,6 +29,7 @@
 
 static int count = 64;
 static secp256k1_context *ctx = NULL;
+static secp256k1_context *sttc = NULL;
 
 static void counting_illegal_callback_fn(const char* str, void* data) {
     /* Dummy callback function that just counts. */
@@ -7390,6 +7391,15 @@ int main(int argc, char **argv) {
         CHECK(secp256k1_context_randomize(ctx, rand32));
     }
 
+    /* Make a writable copy of secp256k1_context_static in order to test the effect of API functions
+       that write to the context. The API does not support cloning the static context, so we use
+       memcpy instead. The user is not supposed to copy a context but we should still ensure that
+       the API functions handle copies of the static context gracefully. */
+    sttc = malloc(sizeof(*secp256k1_context_static));
+    CHECK(sttc != NULL);
+    memcpy(sttc, secp256k1_context_static, sizeof(secp256k1_context));
+    CHECK(!secp256k1_context_is_proper(sttc));
+
     run_rand_bits();
     run_rand_int();