While reviewing D57058, Louis had some questions about the existing span constructor tests. They were not testing the stuff that they said they were. Updated the tests to test what they should have been doing

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@351887 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed