Elixir (UndefinedFunctionError) function in test env

I have this code in the module

alias Commerce.Cart.{Cart, CartMaster}

@spec call(Cart.t()) :: Cart.t()
def call(cart) do
  cart
  |> add_pets_adjustments()
  |> CartMaster.recalculate_credit()
end

when I run the test I get this error

** (UndefinedFunctionError) function Commerce.Cart.CartMaster.recalculate_credit/1 is undefined (module Commerce.Cart.CartMaster is not available)

I checked the CartMaster module and the name is correct

defmodule Commerce.Cart.CartMaster do
  #  ...
  def recalculate_credit(cart) do
    cart
    |> remove_existing_credit_adjustment
    |> remove_applied_credit()
    |> apply_credit()
    |> add_credit_adjustment()
  end
end

I also changed the function call to

def call(cart) do
  cart
  |> add_pets_adjustments()
  |> Commerce.Cart.CartMaster.recalculate_credit()
end

And got the same error

I checked in the "_build/test/lib/app/ebin" and I found the Elixir.Commerce.Cart.CartMaster.beam file

calling the function to check modules loaded inside the call function

:app
|> :application.get_key(:modules)
|> elem(1)
|> Enum.filter(fn e -> String.contains?(to_string(e), "Commerce.Cart") end)
|> IO.inspect(label: :modules)

the module shows in the list

modules: [Commerce.Cart.Adjustment, Commerce.Cart.Cart, Commerce.Cart.CartMaster, ...]

running the app in development mode and doing manual testing works just fine,
I'm out of ideas of what it can be.