Overview

• Quiz.
• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Using testing to assess candidate solutions.
• A problem in testing.
• Some strategies for improving your tests.

Preliminaries

Admin

• Continue lab partners from Wednesday.
• Sam may be late to class today. We'll start with the quiz.
• It's Friday. There's a Harris party this weekend. Be thoughtful about your choices. And if you choose to drink, please don't drink to excess.
• If you get weird error messages when using DrRacket, please let me know what computer you are on. (Any other context helps, too.)

Upcoming Work

• No lab writeup. But please do read through the rest of the testing lab.
• Exam 1 due next Tuesday night.
  • The prologue is due tonight (optional, but recommended).
  • We will quickly step through the questions.
  • You are already up to 4 points of extra credit.
• Reading for Monday:
  • Transforming RGB Colors

Extra Credit Opportunities

Academic

• Convocation next Wednesday
• Campus Town Hall September 30
• CS Table next Thursday: Mathematical Image Synthesis Toolkit

Peer Support

• Football Games (???)
• Men's Tennis (???)
• Women's Tennis (at a tournament this weekend)
• Noteworthy, Sat., Sept 27, 3:30 p.m. Herrick
• Science poster session, Sat., Sept. 27, morningish
• Anna Christie, Oct. 9-12 (SB plays Marthy)
• Evan's awesome radio show at 5pm on KDIC.
• Donna's equally awesome radio show midnight Sunday (heading into Monday).

Miscellaneous

• Participate in #GrinWell.
• Friends of Drake Library needs help setting up for their annual booksale on Thursday, October 2 (conveniently, the same night as Grinnell High School's homecoming parade). You can help a good cause and probably get a few free books, too.

Questions

Using testing to assess candidate solutions

• Testing: Apply the scientific method to programs
  • Hypothesis: Our procedure works
  • Experiments: For these inputs I expect these outputs. Write as prototcol, rather than just working "on the fly"
    • Protocol: "test suite"
  • If they all succeed, we have some confidence
  • If any tests fail, we can reject the procedure
• The lab
  • A good test suite can be applied to any procedure that has the same goals.
  • A good test suite will let you distinguish between correct and incorrect solutions.
  • Goal of lab: Write tests that do this distinguishing.

A problem in testing

• Write a good test suite for classify-triangle
• A good test suite will tell us which of the implementations is wrong.
• First test: Equilateral triangle.
• Second test: Non-triangle, hope that we get an error.

Our code

#lang racket
(require rackunit)
(require rackunit/text-ui)
(require triangles/tri-2200)

(define triangle-tests
  (test-suite 
   "Testing classify-triangle"
   (test-case "not quite an isosceles triangle"
          (check-exn exn:fail? (lambda () (classify-triangle 2 2 5))))
   (test-case "not quite scalene"
          (check-exn exn:fail? (lambda () (classify-triangle 80 60 1))))
   (test-case "zero side length"
          (check-exn exn:fail? (lambda () (classify-triangle 0 0 0))))
   (test-case "an isosceles triangle"
          (check-equal? (classify-triangle 2.0 2.0 3.0) "isosceles"))
   (test-case "an isosceles triangle"
          (check-equal? (classify-triangle 2.0 3.0 2.0) "isosceles"))
   (test-case "an isosceles triangle"
          (check-equal? (classify-triangle 3.0 2.0 2.0) "isosceles"))
   (test-case "a really big equilateral triangle"
          (check-equal? (classify-triangle (expt 2 1000) (expt 2 1000) (expt 2 1000)) "equilateral"))
   (test-case "a really small equilateral triangle"
          (check-equal? (classify-triangle .0000000001 .0000000001 .0000000001 ) "equilateral"))
   (test-case "a scalene triangle"
          (check-equal? (classify-triangle 2 3 4) "scalene"))
   (test-case "unit side length equilateral triangle"
          (check-equal? (classify-triangle 1 1 1) "equilateral"))))