CSC151 2007S, Class 27: Testing Your Procedures

Admin:
* Are there questions on Friday's class?
* Are there questions on Assignment 11?
  * Now Due on Friday
* Reading for tomorrow: Analyzing Algorithms.
* Cool hint: When DrFu crashes, it often leaves your recent
  work around, even when you haven't saved
  * Look in your home directory for #mred...#
  * Use the one with the largest number for the ellipses
* Your TA will be missing class on Thursday and Friday

Overview:
* Why test?
* Strategies for testing.
* Our Unit Testing Framework

/Why Test/

* To "make sure that they're correct"
  * See that it at least works on some examples
  * There are always more tests to run
* Tests give you some confidence that your procedure is correct

(define square
  (lambda (x)
    (* x x)))

Definition looks good
a
> (square 0)
0
> (square -1)
1
> (square 1)
1
> (square 1.5)
2.25
> (square (- 3 5))
4

Lots of tests look good

> (square 2147483648)
1

Whoops.  Failed miserably.

Problem: Multiplication of exact integers only works correctly if the result
is less than 2^31.
* So, a precondition of square should be:
  -sqrt(2^31) < x < sqrt(2^31)

Last week, Microsoft Excel would sometimes say something like 
32675 + 32000 = 100,000
If you divided the result by two, you'd get something close to 32000

/How to Test/
* Every testing strategy has the flaw that "You haven't tested every case"

* Write an expresion, run the program, look at the result
  * Takes a lot of *human* time to look at the results
* Make the computer check!
  * (if (equal? EXPRESSION EXPECTED_RESULT) "OK" "FAILED")
  * Takes a lot of *human* time to look at the results
* Recent strategy: Unit testing
  * Combine tests together.  At the end, report the number of
    successes and failures.
    N tests conducted
    M succeeded
    P failed
    List of tests that failed

In this class, we'll use a few helpful procedures for unit testing
(begin-tests!) - Start the testing framework
(test! exp result) - Run one test to see if it succeeds
(end-tests!) - Report on the tests (as above)

(begin-tests!)
(test! (square 0) 0)
(test! (square 1) 1)
(test! (square -1) 1)
(test-error! (square null))
(end-tests!)$a

Today's goal: Write a procedure that, given three sides, classifies a
triangle
(define classify-triangle
  (lambda (side1 side2 side3)
     ...))
* If it's equilateral, says "equilateral"
* If it's isosceles, says "isosceles"
* If it's any other kind of triangle, says "scalene"
* If it's not a triangle, should crash and burn (that is, report an
  error, not end DrFu)

[01] tri.0000.ss | [04] tri.0001.ss | [X ] tri.0010.ss | [03] tri.0011.ss
[01] tri.0100.ss | [X ] tri.0101.ss | [X ] tri.0110.ss | [  ] tri.0111.ss
[01] tri.0200.ss | [X ] tri.0201.ss | [  ] tri.0210.ss | [  ] tri.0211.ss
[01] tri.1000.ss | [  ] tri.1001.ss | [  ] tri.1010.ss | [02] tri.1011.ss
[01] tri.1100.ss | [  ] tri.1101.ss | [  ] tri.1110.ss | [  ] tri.1111.ss
[01] tri.1200.ss | [01] tri.1201.ss | [  ] tri.1210.ss | [  ] tri.1211.ss
[01] tri.2000.ss | [  ] tri.2001.ss | [  ] tri.2010.ss | [05] tri.2011.ss
[01] tri.2100.ss | [  ] tri.2101.ss | [  ] tri.2110.ss | [  ] tri.2111.ss
[04] tri.2200.ss | [X ] tri.2201.ss | [X ] tri.2210.ss | [  ] tri.2211.ss

Which ones don't work and why?

Notation:
* Blank means "untested"
* [X ] means "failed some test, but I'm not telling you which one"
* [01] means "classified 2 2 3 as scalene, rather than isosceles"
* [02] means "failed to indicate that 1 1 5 is not a triangle"
* [03] means "failed to indicate that 3 7 3 is not a triangle"
* [04] means "failed to classify 1 1 1 as an equilateral triangle"
* [05] means "seems to think 2 2 5 is a triangle"