tests: Replace counting_illegal_callbacks with CHECK_ILLEGAL_VOID

This commit also explicitly initializes shortpubkey. For some reason, removing
surrounding, unrelated lines results in gcc warnings when configured with
--enable-ctime-tests=no --with-valgrind=no.

src/modules/ecdh/tests_impl.h

@@ -25,32 +25,19 @@ static int ecdh_hash_function_custom(unsigned char *output, const unsigned char
 }
 
 static void test_ecdh_api(void) {
-    /* Setup context that just counts errors */
-    secp256k1_context *tctx = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
     secp256k1_pubkey point;
     unsigned char res[32];
     unsigned char s_one[32] = { 0 };
-    int32_t ecount = 0;
     s_one[31] = 1;
 
-    secp256k1_context_set_error_callback(tctx, counting_illegal_callback_fn, &ecount);
-    secp256k1_context_set_illegal_callback(tctx, counting_illegal_callback_fn, &ecount);
-    CHECK(secp256k1_ec_pubkey_create(tctx, &point, s_one) == 1);
+    CHECK(secp256k1_ec_pubkey_create(CTX, &point, s_one) == 1);
 
     /* Check all NULLs are detected */
-    CHECK(secp256k1_ecdh(tctx, res, &point, s_one, NULL, NULL) == 1);
-    CHECK(ecount == 0);
-    CHECK(secp256k1_ecdh(tctx, NULL, &point, s_one, NULL, NULL) == 0);
-    CHECK(ecount == 1);
-    CHECK(secp256k1_ecdh(tctx, res, NULL, s_one, NULL, NULL) == 0);
-    CHECK(ecount == 2);
-    CHECK(secp256k1_ecdh(tctx, res, &point, NULL, NULL, NULL) == 0);
-    CHECK(ecount == 3);
-    CHECK(secp256k1_ecdh(tctx, res, &point, s_one, NULL, NULL) == 1);
-    CHECK(ecount == 3);
-
-    /* Cleanup */
-    secp256k1_context_destroy(tctx);
+    CHECK(secp256k1_ecdh(CTX, res, &point, s_one, NULL, NULL) == 1);
+    CHECK_ILLEGAL(CTX, secp256k1_ecdh(CTX, NULL, &point, s_one, NULL, NULL));
+    CHECK_ILLEGAL(CTX, secp256k1_ecdh(CTX, res, NULL, s_one, NULL, NULL));
+    CHECK_ILLEGAL(CTX, secp256k1_ecdh(CTX, res, &point, NULL, NULL, NULL));
+    CHECK(secp256k1_ecdh(CTX, res, &point, s_one, NULL, NULL) == 1);
 }
 
 static void test_ecdh_generator_basepoint(void) {