Will an algorithm get the entire hidden test data set in one go?ΒΆ

No, Grand Challenge schedules one algorithm job per image set (archive item) in the linked archive.

In a typical challenge this means that an algorithm only ever gets one patient's data at a time (e.g., patient A's CT image and the corresponding mask in the first run, patient B's CT image and mask in the second run etc.).

Each algorithm job is independent because the algorithm container is rebuild from the image for each job. The algorithm can thus not use data or information from other cases.

Also see:
How is the test data provided to the algorithm container?