feat(spannertest): Add validation of duplicated column names (#4611)
feat(spannertest): Add validation of duplicated column names (#4611)

* feat(spannertest): add validation for duplicated column names

* feat(spannertest): fix error message in validation of duplicated column

Co-authored-by: Knut Olav Løite <62634d14bf6dff6edb4b7af974862bb227095f71@gmail.com>

Co-authored-by: Knut Olav Løite <62634d14bf6dff6edb4b7af974862bb227095f71@gmail.com>
googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go