How to mock paging DataSource.Factory for unit tests?

Question

Dao:

@Query("room db query") 
fun getSomeItemsDataSource(): DataSource.Factory<Int, SomeEntity>

i have this query for pagination from my room db table. when i want to mock this or use double test class for DataSource.Factory i can't give any list to return or create an instance from it? I cant write unit tests for my viewmodel neither for my resository. It throws NullPointerException as it should be when i use mock. see the usage below:

Repository:

override fun getSomeItemsDataSource(): DataSource.Factory<Int, SomeEntity> =
someDao.getSomeItemsDataSource()

ViewModel:

val someItems: Flow<PagingData<SomeEntity>> =
        Pager(
            config = PagingConfig(pageSize = 1),
            pagingSourceFactory = someRepository
                .getSomeItemsDataSource()
                .asPagingSourceFactory()
        )
            .flow
            .cachedIn(scope = viewModelScope)