in Sources/_CollectionsTestSupport/MinimalTypes/_CollectionState.swift [178:191]
func remove(count: Int, at offset: Int) {
precondition(count >= 0 && offset >= 0 && offset + count <= self.count)
guard count > 0 else { return }
switch strategy {
case .allIndices:
self.count -= count
case .afterChange:
let rest = offset ..< self.count
self.indexValidity.replaceSubrange(rest, with: repeatElement(id, count: rest.count - count))
self.endIndexValidity = self.id
self.count -= count
assert(indexValidity.count == self.count)
}
}