What does this error mean/how do I fix it?

I’m not sure what this error means or how to fix it, any help would be greatly appreciated!

[code removed - moderator]

In theory, the code is correct. This is because you can specify a metric by name or by instance of a class. Also, if you specify only 1 metric and not a list, tensorflow is smart enough to do the check for list type and proceed accordingly.
This test however, requires you to specify the metric as a list of 1 string. So, please change your code.

Thank you, that worked!