Function ffi_utils::test_utils::call_0_with_custom

pub fn call_0_with_custom<F>(ud: &mut UserData, f: F) -> Result<(), i32> where
    F: FnOnce(*mut c_void, extern "C" fn(user_data: *mut c_void, result: *const FfiResult)), 

Call a FFI function and block until its callback gets called. Use this if the callback accepts no arguments in addition to user_data and error_code. This version of the function takes a UserData with custom inner data.