Add snapshot / unit tests

[PanAeon]

Hi,
I have added some basic unit tests and also some snapshot tests.
Almost all of the code examples I took from the scala spec.

Related Issue #26

[olafurpg]

Fantastic work! I am very excited about having tests, this will make code reviewing changes in the future much easier :)

The text format of the assertions is nice, very easy to read. I am wondering, would it be possible to auto-generate the assertions given a plain Scala source file? We might be able to use the auto-generated assertion files as expect outputs instead of the JSON files. Expect tests should ideally have human readable output files so that the diffs are easier to review.

[PanAeon]

Well, yes. This is what I tried to do at first attempt :) But I think I got some aggregation wrong and end up having overlapping tokens, then I abandoned the idea. Now I looked at it again and I think it's totaly possible. This is how it's gonna look like:

>in  { home       = "/home/${user}"
#^^ source.dhall keyword.control.dhall
#  ^^ source.dhall
#    ^ source.dhall meta.declaration.data.record.block.dhall keyword.operator.record.begin.dhall
#     ^ source.dhall meta.declaration.data.record.block.dhall
#      ^^^^ source.dhall meta.declaration.data.record.block.dhall variable.object.property.dhall
#          ^^^^^^^ source.dhall meta.declaration.data.record.block.dhall
#                 ^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall punctuation.separator.dictionary.key-value.dhall
#                  ^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall
#                   ^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall string.quoted.double.dhall
#                    ^^^^^^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall string.quoted.double.dhall
#                          ^^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall string.quoted.double.dhall constant.other.placeholder.dhall punctuation.section.curly.begin.dhall
#                            ^^^^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall string.quoted.double.dhall constant.other.placeholder.dhall meta.abel.dhall
#                                ^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall string.quoted.double.dhall constant.other.placeholder.dhall punctuation.section.curly.end.dhall
#                                 ^ source.dhall meta.declaration.data.record.block.dhall meta.declaration.data.record.literal.dhall string.quoted.double.dhall

I'll update this pull request once I finished

[olafurpg]

LGTM 👍 Thank you @PanAeon for your hard work.

[olafurpg]

😍 This looks great!