W1A2 assignment issue with code in Ex 2 test cell

Interesting. But that cell is immutable, so how did it get changed? Did you use any external tools on the notebook other than just running it on the course website?

But regardless of how the error occurred, the first thing to try to remedy it would be to get a clean copy of the notebook and then carefully “copy/paste” over any completed work from the damaged notebook. There is a topic about how to do that on the DLS FAQ Thread.