Cannot create a mock function with the same arity as the original function definition

[sillidev]

Hi,

I had below code (got it from Phoenix tutorial) and I used Mimic to simulate Repo.transaction() result

  alias MyApp.Repo

  def complete_order(%ShoppingCart.Cart{} = cart) do
    line_items =
      Enum.map(cart.items, fn item ->
        %{product_id: item.product_id, price: item.product.price, quantity: item.quantity}
      end)

    order =
      Ecto.Changeset.change(%Order{},
        user_uuid: cart.user_uuid,
        total_price: ShoppingCart.total_cart_price(cart),
        line_items: line_items
      )

    Ecto.Multi.new()
    |> Ecto.Multi.insert(:order, order)
    |> Ecto.Multi.run(:prune_cart, fn _repo, _changes ->
      ShoppingCart.prune_cart_items(cart)
    end)
    |> Repo.transaction()
    |> case do
      {:ok, %{order: order}} -> {:ok, order}
      {:error, name, value, _changes_so_far} -> {:error, {name, value}}
    end
  end

If I mock transaction/2, I will get error MyApp.Repo.transaction/2 to be invoked 1 time(s) but it has been called 0 time(s)

MyApp.Repo
      |> expect(:transaction, fn _x, _y -> {:error, "mock", "this is mock error for testing", %{}} end)

However, it works well if I try transaction/1 instead

MyApp.Repo
      |> expect(:transaction, fn _x -> {:error, "mock", "this is mock error for testing", %{}} end)

Is it desired behavior? I expect to mock transaction as arity of 2 which matches its definition.

[edgurgel]

The thing is that you are calling transaction/1 with a multi in your example. So you must stub/expect on transaction/1. transaction/2 will only be called when options are passed in. Ecto.Repo simply defaults to [] if the second argument is not passed.

The link you passed is the callback definition not the actual Repo definition:

https://github.com/elixir-ecto/ecto/blob/18288287f18ce205b03b3b3dc8cb80f0f1b06dbe/lib/ecto/repo.ex#L282C26-L282C53