Function ffi_utils::test_utils::call_1_with_custom

pub fn call_1_with_custom<F, E: Debug, T>(
    ud: &mut UserData, 
    f: F
) -> Result<T, i32> where
    F: FnOnce(*mut c_void, extern "C" fn(_: *mut c_void, _: *const FfiResult, _: T::C)),
    T: ReprC<Error = E>, 

Call an FFI function and block until its callback gets called, then return the argument which were passed to that callback. Use this if the callback accepts one argument in addition to user_data and error_code. This version of the function takes a UserData with custom inner data.