since this deals with ttl (of 10 seconds) you should post a function akin to the one in the readme, that uses :timer.sleep and then tell us what the unexpected behaviour is:

# Now it is ready to be used from any other module. Here is an example:
defmodule MyApp.Test do
  alias MyApp.Cache
  alias Nebulex.Object

  def test do
    Cache.set "foo", "bar", ttl: 2

    "bar" = Cache.get "foo"

    true = Cache.has_key? "foo"

    %Object{key: "foo", value: "bar"} = Cache.get "foo", return: :object

    :timer.sleep(2000)

    nil = Cache.get "foo"

    nil =
      "foo"
      |> Cache.set("bar", return: :key)
      |> Cache.delete(return: :key)
      |> Cache.get
  end
end