BTree in Elixir

btree.ex

defmodule BTree do
  defstruct tree: nil
  
  def new(e), do: %BTree{tree: {e, nil, nil}}

  def insert(%BTree{tree: root}, element) do
    %BTree{tree: do_insert(root, element)}
  end

  defp do_insert(nil, element) do
    {element, nil, nil}
  end

  defp do_insert({e, l, r}, element) when e > element do
    {e, do_insert(l, element), r}
  end

  defp do_insert({e, l, r}, element) when e < element do
    {e, l, do_insert(r, element)}
  end

  defp do_insert({_, _, _} = tuple, _element) do
    tuple
  end

  def search(%BTree{tree: root}, element) do
    do_search(root, element)
  end

  defp do_search(nil, element) do
    false
  end

  defp do_search({e, l, _r}, element) when e > element do
    do_search(l, element)
  end

  defp do_search({e, _l, r}, element) when e < element do
    do_search(r, element)
  end

  defp do_search({_, _, _}, _element) do
    true
  end

end 

btree_tests.exs

defmodule TreesTest do
  use ExUnit.Case

  test "new" do
    assert BTree.new(10) 
      == %BTree{tree: {10, nil, nil}}
  end

  test "insert same" do
    assert BTree.new(10) |> BTree.insert(10)
      == %BTree{tree: {10, nil, nil}}
  end

  test "insert lower" do
    assert BTree.new(10) |> BTree.insert(5)
      == %BTree{tree: {10, {5, nil, nil}, nil}}
  end

  test "insert higher" do
    assert BTree.new(10) |> BTree.insert(15) 
      == %BTree{tree: {10, nil, {15, nil, nil}}}
  end

  test "insert lower then higher" do
    assert BTree.new(10) |> BTree.insert(5) |> BTree.insert(15) 
      == %BTree{tree: {10, {5, nil, nil}, {15, nil, nil}}}
  end

  test "insert higher then lower" do
    assert BTree.new(10) |> BTree.insert(15) |> BTree.insert(5)
      == %BTree{tree: {10, {5, nil, nil}, {15, nil, nil}}}
  end

  test "search empty" do
    assert BTree.search(%BTree{tree: nil}, 1) == false
  end

  test "search found" do
    assert BTree.new(10) |> BTree.search(10)
      == true
  end

  test "search not found" do
    assert BTree.new(10) |> BTree.search(1)
      == false
  end

  test "search higher found" do
    assert BTree.new(10) |> BTree.insert(15) |>  BTree.search(15)
      == true
  end

  test "search lower found" do
    assert BTree.new(10) |> BTree.insert(5) |> BTree.search(5)
      == true
  end

   test "search higher not found" do
    assert BTree.new(10) |> BTree.insert(15) |> BTree.search(20)
      == false
  end

  test "search lower not found" do
    assert BTree.new(10) |> BTree.insert(5) |> BTree.search(1)
      == false
  end
  
end