invariants in a Quixir property test

Question

I've implemented the following prop. test:

  use ExUnit.Case, async: true
  use Quixir

      ptest [half_width: positive_int(), median: int(min: ^half_width)], trace: true, repeat_for: 500 do
        ptest half_width: positive_int(), median: int(min: ^half_width) do
          result = Pullapi.Numbers.median_range(median, half_width)
          f..l = result

          assert l - f == 2 * half_width
        end
      end

with the function:

  @doc """                                                                                                             
  Returns a range specified by a median and half-width.                                                                

  ## Examples                                                                                                          
      iex> Pullapi.Numbers.median_range(10, 4)                                                                         
      6..14                                                                                                            
  """
  @spec median_range(integer, integer) :: Range.t()
  def median_range(median, half_width) when half_width > 0 and median >= half_width do
    min = median - half_width
    max = median + half_width
    min..max
  end

Have I identified the key invariant and properties that should be tested here? I believe I've implicitly tested that the enumerable is an ordered range by pattern matching the returned data structure.