As a college prof, I divide assignments into formative and summative. Some assignments are to help you learn, and you can try again, improve your work, etc. Some are designed to measure what you know at a given point in time -- and the timing matters.

Giving students the chance to learn is important. Expecting them to actually master some skills within a given timeframe is also important. I have a relative in a European system in which changes have been made to allow students to take tests on a class for the next two years. The students are not better off -- it sounds miserable for all.