Testing, Debugging, Exception

Question 1

What can you do to achieve high quality programming?

Answer 1

1. Testing
2. Defensive Programming
3. Eliminate sources of bugs

Question 2

What is defensive programming?

Answer 2

• Write specifications for functions
• Modularize programs
• Check conditions on inputs/outputs

Question 3

What can you do to test your programs?

Answer 3

1. Compare in/outputs

i. e. it’s not working

Question 4

What is debugging?

Answer 4

Study the events leading up to an error

• -> Why is it not working?
• -> How can I fix my peogram?

Question 5

How can you create a good debugging experience?

Answer 5

1. Break program into modules that can be tested and debugged individually
2. Document constraints on modules
   - -> What do you expect the input to be
   - -> what do you expect the output to be?
3. Document assumptions behind code design

Question 6

When are you ready to test?

Answer 6

1. Code has to run!
   - > remove syntax errors
   - -> remove static semantic errors
2. Have a set of expected results

Question 7

What testing classes do we know?

Answer 7

1. Unit testing: Test each function separately
2. Regression testing: Catch reintroduced errors that were previously fixed
3. Integration testing: does the overall program work?

Question 8

What testing approaches do we know?

Answer 8

1. Intuition about natural boundaries
2. Blackbox Testing
3. Glassbox testing

Question 9

What is blackbox testing?

Answer 9

• it is designed without looking at the code
• should be done by someone else than the programmer to avoid implementer bias
• can be reused if implementation changes

Question 10

What is glassbox testing?

Answer 10

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

disadvantages:
- missing paths
- can go through loops randomly many times

Question 11

Can a pass complete test miss a bug?

Answer 11

yes, test boundary cases

Question 12

What are print statements good for?

Answer 12

To test hypothesis
use bisection method:
-> put print halfway in code

Question 13

What are the steps in debugging?

Answer 13

1. Study program code
2. don’t ask whats wrong
3. Ask how did I get an unexpected result
4. Pick simple input to test with

Question 14

When do you get an index error?

Answer 14

I.e. trying to access beyond the limits of a list

Question 15

When do you get an TypeError?

Answer 15

1. trying to convert an inappropriate type i.e. int(test)

2. Mixing data types without appropriate coercion

Question 16

When do you get a NameError?

Answer 16

When you reference a non-existent variable

Question 17

When do you get a syntax error?

Answer 17

python can’t parse the program –> forgetting to close parentheses, quotation etc.

Question 18

When do you get a value error?

Answer 18

the operand is okay but the value is illegal

Question 19

How do you handle exceptions?

Answer 19

Python can provide handlers for exceptions: 
try:
     body - what to do
except : 
     print("Bug in ...")

Question 20

What to do when you encounter an error?

Answer 20

1. Fail silently (bad idea)
2. return an error value
3. stop execution - in python: raise an exception

Question 21

What is an assertion?

Answer 21

1. means of defensive programming
2. use an assert statement
   to raise an AssertionError
   exception if assumptions not met
3. ensure than execution halts whenever expected conditions are met