Two Sources of Bugs

• State
• Behavior

It's either in the data, or in the code

State

• Class attributes
• Input files
• Method arguments

Revealing State

• Print Statements
• Conditional Statements
• Logging
• Debuggers

Forcing State

• Unit Tests
• Sample Inputs
• Hard-coding with extreme caution

Behaviors

• Call Stack
• Debuggers
• Print Statements
• Loggers
• Unit Tests