class_docstr: Coverage
class_docstr_tok: ["Coverage"]
docstr: The size of timestamp col is less than a2 col.
code: def test_time_window_coverage(self):
      """
      The size of timestamp col is less than a2 col.
      """
      p_start = Pipeline.input("a")
      p1 = p_start.flat_map("a", "a1", lambda x: list(range(1, x + 1)))
      p2 = p_start.flat_map("a", "a2", lambda x: list(range(1, x + 4)))
      p = (
          p1.concat(p2)
          .map("a1", "ts", lambda x: x * 1000)
          .time_window("a1", "b", "ts", 3, 3, sum)
          .output("b", "a2")
      )
      res = p(4).to_list()
      self.assertEqual(
          res,
          [
              [3, 1],
              [7, 2],
              [Empty(), 3],
              [Empty(), 4],
              [Empty(), 5],
              [Empty(), 6],
              [Empty(), 7],
          ],
      )
  
imports: import unittest
  from towhee.operator.nop import NOPNodeOperator
  from towhee.operator import PyOperator
  from towhee.runtime.pipeline import Pipeline
  from towhee.runtime.data_queue import Empty
  from towhee.runtime import ops, register
  from towhee.runtime.runtime_pipeline import RuntimePipeline
label_desc: Use image node_id 6 for calling the TestPipelineColCoverage obj's underlying member method code with example usage: obj.test_time_window_coverage() without return types