code: def test_sample_lam_negative(self):
      mm = ManifoldMixup(alpha=-1)
      sl = mm._sample_lam
      lam = sl()
  
      self.assertTrue(lam == 1.0)
  
imports: from unittest import TestCase
  from mock import patch, Mock
  from torch import nn
  from torchbearer.callbacks.manifold_mixup import ManifoldMixup
  import torchbearer
  import torch
label_desc: Use image node_id 16 for calling the TestManifoldMixup obj's underlying member method code with example usage: obj.test_sample_lam_negative() without return types