defoverridable example in elixir

defoverridable.exs

defmodule DefaultModule do
  @callback hello(any()) :: any()

  defmacro __using__(_opts) do
    quote do
      @behaviour DefaultModule

      def hello(:a) do
        :a
      end

      defoverridable DefaultModule
    end
  end
end

defmodule Test do
  use DefaultModule

  def hello(:test) do
    :test
  end
end

IO.puts Test.hello(:test)
Test.hello(:a)

### Output
# mix run defoverridable.exs
# test
# ** (FunctionClauseError) no function clause matching in Test.hello/1
#
#    The following arguments were given to Test.hello/1:

#        # 1
#        :a

#    defoverridable.exs:20: Test.hello/1
#    (elixir) lib/code.ex:677: Code.require_file/2
#    (mix) lib/mix/tasks/run.ex:136: Mix.Tasks.Run.run/5
#    (mix) lib/mix/tasks/run.ex:76: Mix.Tasks.Run.run/1
#    (mix) lib/mix/task.ex:314: Mix.Task.run_task/3