While running i got this error in which it says test your code needs to be defined
Most likely that means you did not run the earlier cells in the notebook, which probably import that function. Try “Cell → Run All Above” and then run that test cell again.
Note that you always need to run all the previous cells anytime you close and reopen or “restart” the notebook.
I have not taken that course, but I would assume there is a lecture or reading item before the first time you use the notebooks which explains how they work, including this point about needed to run the cells in order.
Thankyou @paulinpaloalto it really works!