Chore: stringfy_map/1 changes order of Map keys intermittently.

[nelsonic]

while the Useful.stringfy_map/1 function works to stringify the Map,
the tests assertions fail intermittently because the map keys are being positioned in different order.
Best explained by the following test failures:

 1) test stringfy_map/1 converts nested maps into strings (UsefulTest)
     test/useful_test.exs:199
     Assertion with == failed
     code:  assert Useful.stringify_map(map) == "data__name: Vitor, data__other__data: info, id: 1"
     left:  "id: 1, data__name: Vitor, data__other__data: info"
     right: "data__name: Vitor, data__other__data: info, id: 1"
     stacktrace:
       test/useful_test.exs:201: (test)

  2) doctest Useful.stringify_map/1 (5) (UsefulTest)
     test/useful_test.exs:4
     Doctest failed
     doctest:
       iex> map = %{name: "alex", data: %{age: 17, height: 185}}
       iex> Useful.stringify_map(map)
       "data__age: 17, data__height: 185, name: alex"
     code:  Useful.stringify_map(map) === "data__age: 17, data__height: 185, name: alex"
     left:  "name: alex, data__age: 17, data__height: 185"
     right: "data__age: 17, data__height: 185, name: alex"
     stacktrace:
       lib/useful.ex:142: Useful (module)

  3) test stringfy_map/1 converts nested lists into strings (UsefulTest)
     test/useful_test.exs:204
     Assertion with == failed
     code:  assert Useful.stringify_map(map) == "data__names: \"Vitor, alex\", id: 1"
     left:  "id: 1, data__names: \"Vitor, alex\""
     right: "data__names: \"Vitor, alex\", id: 1"
     stacktrace:
       test/useful_test.exs:206: (test)

This isn't really a "bug" per se. More of an annoying quirk that we need to fix.
Again, the function works but we want the assertions to be 100% consistent.
Therefore ...

Todo

• Alphabetise the Map keys before stringifying them.

[nelsonic]

The function definition was:

useful/lib/useful.ex

Lines 149 to 154 in 370a032

	def stringify_map(map) when is_map(map) do
	map
	|> flatten_map()
	|> Enum.map(&stringify_tuple/1)
	|> Enum.join(", ")
	end

Adding the |> Enum.sort() after the call to flatten_map() did the trick:

  def stringify_map(map) when is_map(map) do
    map
    |> flatten_map()
    |> Enum.sort()
    |> Enum.map(&stringify_tuple/1)
    |> Enum.join(", ")
  end

Ref: https://stackoverflow.com/questions/30627233/sort-list-elements-in-elixir

[nelsonic]

Included in PR: #57