Elixir unit tests next to the source file

Questions & Help Questions
1

i prefer to have my unit tests next to the source file instead of a separate folder. when i run mix test it runs the tests only within the test folder. if i remove the test folder, move the test files, and the give the following configuration in the mix.exs configuration

      test_paths: ".",
      exclude: "deps",
      test_pattern: "*_test.exs",

then it seems to do something different and fails with the following error

(Protocol.UndefinedError) protocol Enumerable not implemented for "." of type BitString. This protocol is implemented for the following type(s): DBConnection.PrepareStream, DBConnection.Stream, Date.Range, Ecto.Adapters.SQL.Stream, File.Stream, Floki.HTMLTree, Function, GenEvent.Stream, HashDict, HashSet, IO.Stream, Jason.OrderedObject, List, Map, MapSet, Range, Stream, Timex.Interval
    (elixir 1.14.3) lib/enum.ex:1: Enumerable.impl_for!/1
    (elixir 1.14.3) lib/enum.ex:166: Enumerable.reduce/3
    (elixir 1.14.3) lib/enum.ex:4307: Enum.each/2
    (mix 1.14.3) lib/mix/tasks/test.ex:529: Mix.Tasks.Test.do_run/3
    (mix 1.14.3) lib/mix/task.ex:421: anonymous fn/3 in Mix.Task.run_task/4
    (mix 1.14.3) lib/mix/cli.ex:84: Mix.CLI.run_task/2

i also tried using tag filters

  @tag mustexec: true
  test "test1" do
  end

and then running ix test --only mustexec but i still get the same error