An example of how not to answer an interview question

I have a bunch of technical questions I typically ask candidates. One of which deals with threading and goes like this:

The following code is being executed in a highly threaded environment.
1. Why does the Debug.Assert statement sometimes fail?
2. What can be done to stop this from occurring?

public class Warehouse
{
 private  int stockCount = 0;
 public void DecrementStock ()
 {
  if ( stockCount > 0 )
    stockCount--;
  Debug.Assert ( stockCount >= 0 )
 }
 public void IncrementStock()
 {
   stockCount ++;
 }
}

The answer is a beauty:

Remove the code in decrementing the stock… this would make the condition of Debug.Assert to always true.

What a great answer - if in doubt, delete the code. As long as the Assert validates then the system must be correct. Why, even the unit tests would all work then. Genius!!