The Correct Way to Debug

Do the opposite of devil debugging...

• Scatter print statements everywhere
• Try things at random till the bug goes Proceed systematically
• Never backup earlier versions Backup everything (use git!)
• Don't bother understanding what the program should do Understand what the program should do
• Use the most obvious fix - fix the symptom not the problem (e.g. hack in the right answer) Fix the problem, not the symptom

You should...

• Understand what the problem is
• Understand what the code should do
• Be able to predict how the fix will address the problem (the cause not the symptom)

Failures, Errors and Defects

Definitions

• Errors Things that are not correct, right or true.
• Failures A problem that is visible by the user resulting from an error in the code.
• Defects are errors that are hidden within the code. It turns valid input into a failure. (Also known as a fault, or a bug).

Propagation

• Defects lead to 'infections'
• Infections can be propagated to further infections
• Infections may die out
• Infections can be lead to a failure