code: def test_insert_in_background_transitions_start(self):
      new_src_segments, new_dst_segments = helpers.compute_segments(
          "insert_in_background",
          src_duration=20.0,
          dst_duration=26.0,
          src_fps=25,
          dst_fps=30,
          metadata=None,
          offset_factor=0.0,
          background_video_duration=10.0,
          source_percentage=None,
          transition_before=False,
          transition_after=True,
          transition=af.TransitionConfig(
              effect=af.TransitionEffect.CIRCLECLOSE, duration=4.0
          ),
      )
      self.assert_equal_segment_lists(
          new_src_segments, [Segment(start=0.0, end=18.0)]
      )
      self.assert_equal_segment_lists(
          new_dst_segments, [Segment(start=0.0, end=18.0)]
      )
  
imports: import os
  import unittest
  from typing import List
  from unittest.mock import MagicMock, patch
  from augly.utils import Segment
  from augly.utils.base_paths import ASSETS_BASE_DIR
  from augly.video import helpers
  from augly.video.augmenters import ffmpeg
label_desc: Use image node_id 3 for calling the MetadataUnitTest obj's underlying member method code with example usage: obj.test_insert_in_background_transitions_start() without return types