The Swedish version of this site is authoritative if this translation differs from it.
What happens if I'm late?
If you arrive after the test has started, you risk not being let in. You would then normally have to wait for a later test date.
Supervised tests have fixed start times. Once the test has begun, no more people can normally be let in, since it disturbs others and risks test security.
If something unexpected happens on the way — contact the test venue if there are contact details in the summons, but don't count on being allowed to take the test anyway.