class_docstr: test lr scheduler plot.
code: def test_step_lr(self):
      lr_scheduler = StepLR(self.optimizer, step_size=2, gamma=0.1)
      plot_lrs_for_scheduler(
          self.optimizer, lr_scheduler, total_steps=10
      )
  
imports: import unittest
  import torch
  from pathlib import Path
  from torchvision import transforms
  from torchvision.models import resnet18
  from towhee.utils.pil_utils import PILImage
  from towhee.utils.matplotlib_utils import matplotlib
  from towhee.trainer.utils.plot_utils import image_folder_sample_show, image_folder_statistic, show_transform, plot_lrs_for_config, plot_lrs_for_scheduler, interpret_image_classification
  from towhee.trainer.training_config import TrainingConfig
  from torch import nn
  from torch.optim.lr_scheduler import StepLR
label_desc: Use image node_id 2 for calling the TestVisualizationLRScheduler obj's underlying member method code with example usage: obj.test_step_lr() without return types