 self.test("\(testNamePrefix).prefix(upTo:)/semantics") {
   for test in prefixUpToTests {
     let c = makeWrappedCollection(test.collection.map(OpaqueValue.init))
-    let index = c.startIndex.advanced(by: numericCast(test.end))
+    let index = c.advance(c.startIndex, by: numericCast(test.end))
     let result = c.prefix(upTo: index)
     expectEqualSequence(test.expected, result.map(extractValue).map { $0.value },
       stackTrace: SourceLocStack().with(test.loc))

    let survivingIndices =
      Array(
        slice.startIndex ..<
        slice.endIndex.advanced(by: numericCast(-test.numberToRemove))
      )
    let removedElement = slice.popLast()!
    expectEqual(

    let index = c.startIndex
    if resiliencyChecks.creatingOutOfBoundsIndicesBehavior == .trap {
      expectCrashLater()
      _blackHole(c.advance(index, numericCast(-outOfBoundsIndexOffset)))
    } else {
      expectFailure {
        _blackHole(c.advance(index, numericCast(-outOfBoundsIndexOffset)))
      }
    }
  }
