code: def test_with_no_valid_triplets(self):
      loss_func = AngularLoss(alpha=40)
      for dtype in TEST_DTYPES:
          embedding_angles = [0, 20, 40, 60, 80]
          embeddings = torch.tensor(
              [angle_to_coord(a) for a in embedding_angles],
              requires_grad=True,
              dtype=dtype,
          ).to(
              TEST_DEVICE
          )  # 2D embeddings
          labels = torch.LongTensor([0, 1, 2, 3, 4])
          loss = loss_func(embeddings, labels)
          loss.backward()
          self.assertEqual(loss, 0)
  
file_path: pytorch-metric-learning/tests/losses/test_angular_loss.py
imports: import unittest
  import numpy
  import torch
  from pytorch_metric_learning.losses import AngularLoss
  from ..None import TEST_DEVICE, TEST_DTYPES
  from ..zzz_testing_utils.testing_utils import angle_to_coord
  from .utils import get_triplet_embeddings_with_ref
label_desc: Use image node_id 4 for calling the TestAngularLoss obj's underlying member method code with example usage: obj.test_with_no_valid_triplets() without return types