Function ffi_utils::test_utils::call_vec_u8

pub unsafe fn call_vec_u8<F>(f: F) -> Result<Vec<u8>, i32> where
    F: FnOnce(*mut c_void, extern "C" fn(user_data: *mut c_void, result: *const FfiResult, _: *const u8, _: usize)), 

Call a FFI function and block until its callback gets called, then copy the byte array argument which was passed to Vec<u8> and return the result.