def test_invalid_scalar_index(adata, index):
    # https://github.com/theislab/anndata/issues/619
    with pytest.raises(IndexError, match=r".*index.* out of range\."):
        _ = adata[index]
def dfs(self,candidates,target,start,reslist):
        length = len(candidates)
        if target == 0: 
            return self.result.append(reslist)