code: def test_fps(self):
      pos = torch.randn((10, 3))
      batch = torch.zeros(10).to(torch.long)
      sampler = FPSSampler(ratio=0.5)
      self.assertEqual(sampler(pos, batch).shape[0], 5)
  
      sampler = FPSSampler(num_to_sample=5)
      self.assertEqual(sampler(pos, batch).shape[0], 5)
  
file_path: torch-points3d/test/test_sampler.py
imports: import unittest
  import torch
  from torch_geometric.data import Data
  from torch_points3d.core.spatial_ops import FPSSampler, RandomSampler, RadiusNeighbourFinder, MultiscaleRadiusNeighbourFinder
  from torch_points3d.modules.VoteNet.dense_samplers import FPSSamplerToDense
label_desc: Use image node_id 1 for calling the TestSampler obj's underlying member method code with example usage: obj.test_fps() without return types