CSC323 2010S, Class 10: Unit Testing

Overview:
* Project Discussion.
* About Unit Testing and Test-Driven Development.
* Beautiful Testing.
* PyUnit: Unit Testing in Python.
* Lab: Unit Testing.

Admin:
* For Tuesday: Choose a fun model for iSimGrinL
  * Maybe express as use cases.
* Readings for Tuesday
  Skim Chapters 1 and 2 of Version Control with Subversion (for Subversion 1.5); 
  Read BC 2: Subversion's Delta Editor.
* At times, I felt like I read something different than the rest of you.
* So sad.  Escher is gone.  It's because of STUDENTS!
* EC: Today's CS Extra.
* EC: Tomorrow's CS Table.

Project Ideas:
* No, we are not doing an MP3 database.
* No, we are not doing "nevermind I forgot"

Project Decision: Networked, Competitive/Cooperative, Sim game
* What will be the primary creatures in the system?
  * Viruses?  No
  * Fish? No
  * Bugs? Maybe
  * Grinnellians?  Professors, Students, Staff, Townies, Squirrels
    * Has some fun with subclassing and interfaces and ...
* What does networked mean?
  * Direct competition?
  * Multiple copies of creatures that propagate from system to system.
  * A central world that clients connect to?
* What is the goal of the game?

Unit Testing and Test-Driven Development
* Testing should be at the center of your software development process, not an afterthought
* Unit testing: Testing a function against a variety of inputs to make sure that you get what you expect it to do (and that it fails when you expect it to fail)

Why write tests?
* Gives you some confidence that your program works.
* If you do unit testing on every unit, you have confidence that all the parts of your program work individually.
* The book claims that tests can help you think more carefully about
  your code and may even encourage you to rewrite it.
* Test PERMIT you to rewrite your code.
* Tests document expectations.
* Good tests permit automatic testing.

Why write tests first?
* Helps you think more carefully about the requirements of the program.
* Writing tests later can bias you about the tests.
* Write code to meet tests rather than tests to meet code.
* Evidence suggests "I'll do it later" becomes "later than release".

To test well, we need
* Methodology that uses testing (e.g., test-driven development, most
  of the agile methodologies)
* Methodology for writing good tests
* Framework that makes it easier to write and run test suites

The standard framework
* Build test cases
* Tie them together into a hierarchy of test suites

Simple test case: Explore fractions
* Build the fractions 1/2, 1/3, 1/6, and 5/6
* Verify 1/2 * 1/3 = 1/6
* Verify 1/3 * 1/2 = 1/6
* Verify 1/6 / 1/2 = 1/3
* Verify 1/2 + 1/3 = 5/6
* Verify 5/6 - 1/2 = 1/3
* Etc.

Before running tests, you often need to build some values

Test case:
* Build data
* Run tests
* Clean up data

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* Sam goes over questions from students
* Can we generate a random sorted array of size N faster than
  in O(N) steps?
* Start with some number (negative or positive, random)
  * Repeatedly add a random non-negative number to the previous number 
    to generate the next number
* Problem: Might go over MAX_VALUE
  * Choose a smaller range for the next value.
    values[i] = random(MAX_VALUE - values[i-1])
    * Doesn't work if values[i-1] is negative.
    * Clever tricks will help
  * Not really a random distribution, but probably close enough.

Is testing beautiful?
* Beautiful parts
  * Our author thinks that random testing is beautiful for sniffing
    out problems
  * Testing is beautiful, it's like a painter stepping back from a
    canvas
  * Good testing helps you work in situations you can't imagine
* Ugly parts
  * Random testing seems much less nice than systematic testing
  * O(nlogn) per random test.
  * Most programmers don't write comprehensive tests
* Lessons
  * JUnit is simple enough that we should use it all the time and
    teach it in 207.
  * Try to write comprehensive tests (but be careful with your time)

Questions

* Write a simple set of unit tests for a subset of Python's 
  numeric operations.
  * How might you check whether sqrt is appropriate?
* Write a test suite for the sort operation.