code: def test_bmap_effect_trail_length(fake_writer):
      bmap = (
          BMap()
          .add_schema(
              baidu_ak=FAKE_API_KEY, center=[-0.118092, 51.509865]
          )
          .add_coordinate("London", -0.118092, 51.509865)
          .add(
              "bmap",
              [list(z) for z in zip(TEST_LOCATION, TEST_VALUE)],
              type_=ChartType.LINES,
              effect_opts=opts.EffectOpts(trail_length=0.5),
              label_opts=opts.LabelOpts(formatter="{b}"),
          )
      )
      bmap.render("render.html")
      content = fake_writer.call_args[0][1]
      assert_in(
          '"trailLength": 0.5',
          content,
          "trainLength parameter is error",
      )
  
file_path: pyecharts/test/test_bmap.py
imports: from unittest.mock import patch
  from nose.tools import assert_in
  from pyecharts import options
  from pyecharts.charts import BMap
  from pyecharts.globals import BMapType, ChartType
label_desc: Use image node_id 3 for calling a global function with example usage: test_bmap_effect_trail_length(fake_writer) without return types