Issue #3076797 by Wim Leers, lauriii, alexpott:...
Issue #3076797 by Wim Leers, lauriii, alexpott: \Drupal\Core\Extension\Extension's absence of validation has allowed multiple incorrect tests to be added
assert($pathname==='core/core.info.yml'||($pathname[0]!=='/'&&file_exists($root.'/'.$pathname)),sprintf('The file specified by the given app root, relative path and file name (%s) do not exist.',$root.'/'.$pathname));