test: added first unit tests

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🛠 Tooling: Add initial tests scaffolding #4
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Adds tests, including usage of @typescript/vfs for type system tests.

[codecov-commenter]

Codecov Report

Merging #6 (0fabe82) into main (c9dc754) will increase coverage by 25.31%.
The diff coverage is 100.00%.

❗ Current head 0fabe82 differs from pull request most recent head 8f38329. Consider uploading reports for the commit 8f38329 to get more accurate results

@@            Coverage Diff             @@
##            main       #6       +/-   ##
==========================================
+ Coverage   0.00%   25.31%   +25.31%     
==========================================
  Files         12       13        +1     
  Lines        225      237       +12     
  Branches      95       98        +3     
==========================================
+ Hits           0       60       +60     
+ Misses       225      174       -51     
- Partials       0        3        +3     

Impacted Files	Coverage Δ
src/test/utils.ts	100.00% <100.00%> (ø)
src/compilerOptions.ts	84.21% <0.00%> (+84.21%)	⬆️
src/nodes/typeGuards.ts	90.90% <0.00%> (+90.90%)	⬆️
src/syntax.ts	91.66% <0.00%> (+91.66%)	⬆️
src/types/typeGuards.ts	100.00% <0.00%> (+100.00%)	⬆️

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