Remove dependency on XCTest
### Motivation:
As 6.1 does not include XCTest anymore, finish the migration to Swift
testing
### Modifications:
Replace XCTest by Swift Testing in two files
### Result:
`swift test` works on 6.1.2
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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
