fix(test): fix mutation test not actually reading tsconfig

[rubiesonthesky]

PR Checklist

• Addresses an existing open issue: fixes 🛠 Tooling: Codecov action isn't uploading coverage #1454
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

• Refactor file reading in testSetup.ts
• Fix reading tsConfig settings

Some files changed to be what they should be, and some are now exposing bugs (test/cases/fixes/incompleteTypes/returnTypes/expected.ts) .

I'm not sure why the type is being removed in test/cases/fixes/noInferableTypes/variableDeclarations/expected.ts but I think this is also exposing some type. Or it may be that Map would need some different tsconfig settings. - Filed new issue about it #1512

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.62%. Comparing base (b5bfd34) to head (6372fd3).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1511       +/-   ##
===========================================
+ Coverage   28.37%   78.62%   +50.25%     
===========================================
  Files         175      175               
  Lines       10957    10957               
  Branches       50     1021      +971     
===========================================
+ Hits         3109     8615     +5506     
+ Misses       7848     2338     -5510     
- Partials        0        4        +4     

Flag	Coverage Δ
mutation	73.24% <ø> (?)
unit	28.37% <ø> (ø)

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[rubiesonthesky]

I'm merging this to get the benefit for other fixes. But I'm up for fixing / improving the code in follow-ups.

[JoshuaKGoldberg]

Thanks - I've been a little slammed this month, sorry for not responding quickly. 🙂