code: def test_flatten():
      assert flatten([]) == []
      assert flatten([[]]) == []
      assert flatten([[], []]) == []
      assert flatten([[], [3]]) == [3]
      assert flatten([[1, 2, 3], [3], [4, 5]]) == [1, 2, 3, 3, 4, 5]
      assert flatten([["a", "b", "c"], ["d", "e"]]) == [
          "a",
          "b",
          "c",
          "d",
          "e",
      ]
      assert flatten([[["a"], ["b"]], [[1, 2, 3], [4, 5]]]) == [
          ["a"],
          ["b"],
          [1, 2, 3],
          [4, 5],
      ]
      assert flatten([["apples"], ["bannanas"], ["oranges"]]) == [
          "apples",
          "bannanas",
          "oranges",
      ]
      assert flatten(
          [["apple", "bannana"], ["a", "b", "c"], [1, 2, 3, 4]]
      ) == [
          "apple",
          "bannana",
          "a",
          "b",
          "c",
          1,
          2,
          3,
          4,
      ]
      assert flatten(
          [["apples"], [""], ["bannanas"], [""], ["oranges"], [""]]
      ) == [
          "apples",
          "",
          "bannanas",
          "",
          "oranges",
          "",
      ]
  
imports: from hailtop.utils import partition, url_basename, url_join, url_scheme, url_and_params, parse_docker_image_reference, grouped
  from hailtop.utils.utils import digits_needed, unzip, filter_none, flatten
label_desc: Use image node_id 24 for calling a global function with example usage: test_flatten() without return types