defmodule MyApp.MyMod do
  def value do
    1
  end

  def indirect_value do
    value()
  end
end

defmodule MyApp.MyModTest do
  use ExUnit.Case, async: false
  import Mock

  alias MyApp.MyMod

  test "test" do
    # these two work, obviously
    assert MyMod.value == 1
    assert MyMod.indirect_value == 1

    # in this block, the second assertion fails with:
    # (UndefinedFunctionError) function MyApp.MyMod.indirect_value/0 is undefined (module MyApp.MyMod is not available)
    # I guess this is to be expected, although unintuitive
    with_mock MyMod, [value: fn -> 2 end] do
      assert MyMod.value == 2
      assert MyMod.indirect_value == 2
    end

    # and in this block (adding :passthrough), the second assertion fails, because the indirect_value function still returns 1
    with_mock MyMod, [:passthrough], [value: fn -> 2 end] do
      assert MyMod.value == 2
      assert MyMod.indirect_value == 2
    end
  end
end