🧪 Testing: Use virtual file system in updateLocalFiles.test.ts

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

#1078 applied some improvements to how find-and-replaces via replace-in-file are applied to local files. At the time it was hard to unit test those changes because replace-in-file didn't support a "virtual" (in-memory) file system that tests could use to simulate reading & writing files. A couple of test snapshots now just have [Function] instead of testing what that function reads & writes:

create-typescript-app/src/steps/updateLocalFiles.test.ts

Line 246 in c3f93db

"to": [Function],

But, good news! adamreisnz/replace-in-file#175 -> adamreisnz/replace-in-file#177 added support for that virtual fs to replace-in-file. So now the tests should be able to assert on the actual contents of files in memory by providing their own fs object!

Additional Info

I bet createJoshuaKGoldbergReplacement.test.ts could be improved by a virtual file system too...