Don't actually CHECK in tests in COVERAGE mode

Author: real-or-random

src/util.h

@@ -25,7 +25,11 @@ static SECP256K1_INLINE void secp256k1_callback_call(const secp256k1_callback *
     cb->fn(text, (void*)cb->data);
 }
 
-#ifdef DETERMINISTIC
+#if defined(COVERAGE)
+/* Do nothing in COVERAGE mode. This will make the compiler optimize away the actual branch,
+   and we get useful branch coverage within our test files.  */
+#define TEST_FAILURE(msg)
+#elif defined(DETERMINISTIC)
 #define TEST_FAILURE(msg) do { \
     fprintf(stderr, "%s\n", msg); \
     abort(); \