doctests for randomly generated values

Given the following code:

defmodule Pullapi.Workout do                                                                                     
  import Pullapi.Numbers

  @moduledoc """                                                                                                 
  Functions that generate a workout representation                                                               
  """

  @doc """                                                                                                       
  Returns a pullup set defined by the number of `max_reps` a user can do, a `percentage`, and the                
  number of maximum additional or decremented reps, `rep_bound`.                                                 

  ## Examples                                                                                                    
  iex> Pullapi.Workout.pullup_set(20, 60, 5)                                                                     
  %{"Action" => "Pullups", "Units" => "14"}                                                                      
  """
  @spec pullup_set(integer, integer, integer) :: map()
  def pullup_set(max_reps, percentage, rep_bound) do
    median = max_reps * (percentage / 100)
    unit_range = Pullapi.Numbers.median_range(round(median), rep_bound)
    units = Enum.random(unit_range)

    %{"Action" => "Pullups", "Units" => "#{units}"}
  end
end

The doctest fails with:

  1) test doc at Pullapi.Workout.pullup_set/3 (1) (PullapiTest)
     test/pullapi_test.exs:4
     Doctest failed
     code: Pullapi.Workout.pullup_set(20, 60, 5) === %{"Action" => "Pullups", "Units" => "14"}
     left: %{"Action" => "Pullups", "Units" => "8"}
     stacktrace:
       lib/pullapi/workout.ex:13: Pullapi.Workout (module)

Is there a way of specifying that the "Units" value is randomly generated? It looks like I'm following the way Enum.random is doctested