test("combine of some leaf list") {
    val leaflist = List(Leaf('e', 1), Leaf('t', 2), Leaf('x', 4))
    assert(combine(leaflist) === List(Fork(Leaf('e',1),Leaf('t',2),List('e', 't'),3), Leaf('x',4)))
  }

  test("combine of some leaf list 2") {
    val leaflist = List(Leaf('e', 1), Leaf('t', 2))
    assert(combine(leaflist) === List(Fork(Leaf('e',1),Leaf('t',2),List('e', 't'),3)))
  }