Good Programming

• Specifications for functions • Modularize programs • Check conditions on input/outputs (assertions)

• Compare input/output to specs • It’s not working! • How can I break my program?

• Study events leading up to the error • Why is it not working? • How can I fix my program?

• design code to ease this part • break programs into modules that can be tested and debugged individually • document assumptions

Ensure code runs - remove syntax errors - remove static semantic errors - Python Interpreter can usually find these Set of Expected results - and input set - for each input a corresponding output

• Unit testing • Regression testing • Integrations testing

• validate each piece of the program - testing each function separately

• add test for bugs as you find them in a function - catch reintroduced errors that were previously fixed

• does overall program work? - tend to rush to do this

• Intuition • Random testing • Black Box Testing • Glass Box Testing

Pick natural boundaries to the problem

If no natural partitions • Probability that code is correct increases with more test • Better options with Black Box and Glass Box

Explore paths through specifications

Explore paths through code

• Designed without looking at the code • Avoid biases implementations • Testing can be reused Paths through specification • build test cases in different natural space partitions

• empty lists • singleton lists • large numbers • small numbers

• Use code directly to guide design of test cases - Called path-complete if every potential path through code is tested at least once

• can go through loops arbitrary many times - missing paths

Branches - exercise all parts of a conditional for loops - loop not entered - body of loop executed exactly once - body of loop executed more than once while loops - same as for loops

• Overt • Covert • Persistent • Intermittent

• Has an obvious manifestation - Code crashes or runs forever

• Has no obvious manifestation - Code returns a value, which may be incorrect but hard to determine

• Occurs every time code is run

• Only occurs some times - even if run on same input