A few reasons not to do testing



It’s boring


Code is just a one off throwaway

As with most research codes

No time for it

A bit more code, a lot less debugging

Tests can be buggy too

See above

Not a professional programmer

See above

Will do it later

See above

A few reasons to do testing

  • lazyness testing saves time

  • peace of mind tests (should) ensure code is correct

  • runnable specification best way to let others know what a function should do and not do

  • reproducible debugging debugging that happened and is saved for later reuse

  • code structure / modularity since the code is designed for at least two situations

  • easier to modify since results can be tested

Not a panacea

Trying to improve the quality of software by doing more testing is like trying to lose weight by weighting yourself more often. - Steve McConnell

  • Testing won’t corrrect a buggy code

  • Testing will tell you were the bugs are…

  • … if the test cases cover the bugs

Tests at different scales

Level of test

Area covered by test

Unit testing

smallest logical block of work (often < 10 lines of code)

Component testing

several logical blocks of work together

Integration testing

all components together / whole program

  • Always start at the smallest scale!

  • If a unit test is too complicated, go smaller.

Legacy code hardening

  • Very difficult to create unit-tests for existing code

  • Instead we make a regression test

  • Run program as a black box:

setup input
run program
read output
check output against expected result
  • Does not test correctness of code

  • Checks code is as similarly wrong on day N as day 0

Testing vocabulary

  • fixture: input data

  • action: function that is being tested

  • expected result: the output that should be obtained

  • actual result: the output that is obtained

  • coverage: proportion of all possible paths in the code that the tests take

Branch coverage:

if energy > 0:
    ! Do this 
    ! Do that

Is there a test for both energy > 0 and energy <= 0?