A friend was "burned" when starting to learn Python, and now sees the language as perhaps fatally flawed.
He was using a library and changed the value of an object's attribute (the class being in the library), but he used the wrong abbreviation for the attribute name.  It took him "forever" to figure out what was wrong.  His objection to Python is thus that it allows one to accidentally add attributes to an object.
Unit tests don't provide a solution to this.  One doesn't write unit tests against an API being used.  One may have a mock for the class, but the mock could have the same typo or incorrect assumption about the attribute name.
It's possible to use __setattr__() to guard against this, but (as far as I know), no one does.
The only thing I've been able to tell my friend is that after several years of writing Python code full-time,  I don't recall ever being burned by this.  What else can I tell him?
I think your friend has misplaced his frustration in the language. His real problem is lack of debugging techniques. teach him how to break down a program into small pieces to examine the output. like a manual unit test, this way any inconsistency is found and any assumptions are proven or discarded.
Protection from accidentally misnaming object attributes in Python?