[WIP] Add tests for BandAid and Suggestions, fix #18

[KuabeM]

What does this PR accomplish?

Bugfix: closes #18 .

Changes proposed by this PR:

Added unit tests for BandAid to find root cause of #18

Notes to reviewer:

This is a very early draft. I just started adding some tests. I need more thorough understanding of the internals of Suggestion and the corresponding processing of from Strings/Literals into BandAids.

Contributor Checklist

• cargo test
• Run cargo spellcheck on the demo dir and verify output manually
• cargo fix && cargo fmt
• cargo spellcheck on the source tree (optional)

Reviewer Checklist

• Code reviewed
• Tests reviewed
• Documentation reviewed

[drahnr]

It's kinda shitty, but gives an overview how things work

                              Documentation

                         +---------------------+
                         |                     |
                         |     LiteralSets     |
                         |  +------------+     |                      +----------------+
   +--------------+      |  |----------------+ |                      |                |
   |              |      |  |---------------------------------------->+   checker1     +------------+
   |              |      |  |--|Literal  |-| | |                      |                |            v
   |   rust       |      |  |--|Literal  |-| | |                      +----------------+          +-------------+
   |              +------------|Literal  |-| | |                                                  |             |
   |              |      |  |--|  +      |-| | |                                                  |  suggestion |
   |              |      |  |--|  |      |-| | |                      +----------------+          +--^----------+
   |              |      |  |--|  |      |--------------------------->+                |             |     |
   |              |      |  |--|  |      |-| | |                      |   checker2     +-------------+     |
   |              |      |  |--------------| | |                      |                |                   |
   |              |      |  +--------------| | |                      +----------------+                   |
   |              |      |     +-------------+ |                                                           |
   +----^---------+      |        |            |                                                           |
        |                |        |            |                                                           |
        |                +---------------------+                                                           |  user picks
        |                         |                                                                        |
        |                         |                                                                        |  replacement
        |                         |                                                                        |
        |                         |                                                                        |
        |                         |                                                                        |
        |                         |                                                                        |
        |                         |                                                                        |
        |                         |                                                                        |
        |                         |                                                                        |
        |                         |                                                                        |
        |                         | original literal span                                                  v
        |                         |                                                                 +----------------+
        |                         |                                                                 |                |
        |                         |                                                                 |                |
        |                         |                                                                 |                |
        |                         |                                                                 |                |
        |                         |                                                                 +----------------+
        |                         |                                                                       |
        |                         |                                                                       |
        |                         |                                                                       |
        |                         |                                                                       |
        |                  +----<-+                                                                       |
        |        BandAid |   |                             range/span within the extracte literal str   |
      <--------------------+   +<-------------------------------------------------------------------------+
                           |   |
                           +---+

[KuabeM]

closed in favor of #53