Add tests for empty strings.
Add tests for empty strings.

pedrosnk/elixir,gfvcastro/elixir,elixir-lang/elixir,gfvcastro/elixir,joshprice/elixir,ggcampinho/elixir,lexmag/elixir,beedub/elixir,ggcampinho/elixir,kimshrier/elixir,beedub/elixir,kimshrier/elixir,antipax/elixir,antipax/elixir,lexmag/elixir,kelvinst/elixir,pedrosnk/elixir,kelvinst/elixir,michalmuskala/elixir