Add tests for IEx.Helpers.import_file/1 with missing file
Add tests for IEx.Helpers.import_file/1 with missing file

Added (failing) tests to show how the `IEx.Helpers.import_file/1` macro behaves
when the given file is missing. These tests are failing since they test the
future behaviour of `import_file/1` which will accept an `:optional` option.

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