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

    let index = c.endIndex
    if resiliencyChecks.creatingOutOfBoundsIndicesBehavior == .trap {
      expectCrashLater()
      _blackHole(index.advanced(by: numericCast(outOfBoundsIndexOffset)))
    } else {
      expectFailure {
        _blackHole(index.advanced(by: numericCast(outOfBoundsIndexOffset)))
      }
    }
  }

self.test("\(testNamePrefix).suffix(from:)/semantics") {
  for test in suffixFromTests {
    let c = makeWrappedCollection(test.collection.map(OpaqueValue.init))
    let index = c.advance(c.startIndex, by: numericCast(test.start))
    let result = c.suffix(from: index)
    expectEqualSequence(test.expected, result.map(extractValue).map { $0.value },
      stackTrace: SourceLocStack().with(test.loc))
