General Debugging

Understand the System

• Read the documentation from cover-to-cover to understand how to get the results you want
  • Go in depth on things applicable at the moment
• Know your roadmap
  • Understand what is black box and what is not
• Understand your debugging tools 
  • What tools do you have in order to solve the issue? Learn them in detail. 
  • Do debug logs exist?

Make it Fail

• Do it again so you can look at it, focus on the cause, and know when it is fixed
• Start at the beginning, at a known state that is reliable.
• Simulate the conditions that stimulate the failure. 
  • Its fine to recreate the environment of failure to an extent, but at some point the failing system may not be identical to the recreated environment. 
• Record everything and find the signature of intermittent bugs

Quit Thinking and Look

• Looking is hard, in Software Code it means put in breakpoints, add debug statements, monitoring program values, and examining memory. In Data, it means look at the data manually
• Guess only to narrow the search, but always look to make sure that is indeed the issue
• Build tools to insure that it is fixed

Divide and Conquer

• Narrow the search with successive approximation. 
• Determine which side the bug is on
• Use easy-to-spot test patterns
• Start with the bad/bug and go backwards

Change One Thing at a Time 

• Isolate the key factor
• Change one test at a time and remember to revert back to the state if the change did not fix
• Compare with a good one
• Determine what you changed since the last time it worked properly

Keep and Audit Trail

• Document what you did, in what order, and what happened as a result
• Any detail could be an important one
• Correlate events.
  • "It made noise for four seconds starting at 21:04:53" is better than "it made noise"

Check the Plug

• Question your assumptions
  
  • Are you running the latest code?
• Start at the Beginning
  • Is it plugged in to power? Is power working to begin with?
  • Is the correct input going through?
• Test the Tool
  • Does it work on others?

Get a Fresh View

• Ask for fresh insights
  • Coworkers is all around you, and consider tracking down an expert
• Report Symptoms, Not theories
  • See if a colleague can reach same conclusion without telling them your conclusion

If you Didnt Fix it, It Ain't Fixed

• Check to see if its really fixed
• Problems do not go away by itself
• Learn from the fix, and design better in the future