You probably have done the same when you did revision just before a geography test at school - you probably only learnt the syllabus rather than going to the library and learning everything in the geography section.

The VW engineers made a car that had only 'revised' enough to do well in the test, not to do well in the real world. Here is another example of engineers doing the same in a different industry[1].

[1]: http://omattos.com/2021/11/11/appliancegate-the-energy-effic...