Held: Friday, 19 September 2014

Back to Outline 12 - Raster Graphics and RGB Colors. On to Outline 14 - Transforming Colors.

Summary

We continue our exploration of testing.

Related Pages

• Reading: Testing Your Procedures
• Lab: Unit Testing with RackUnit
• EBoard (Source) (HTML)

Overview

• Using testing to assess candidate solutions.
• A problem in testing.
• Some strategies for improving your tests.

Administrivia

• 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.
  • 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 (???)
• Noteworthy, Sat., Sept 27, 3:30 p.m. Herrick
• Anna Christie, Oct. 9-12 (SB plays Marthy)

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.

Using testing to assess candidate solutions

• Standard testing model:
  • Hypothesis: This procedure is correct.
  • Experiment: If the procedure is correct, it should have this behavior on these inputs.
    • Ideally, write in such a way that it's easy to rerun: Protocol in bench science, test suite in CS.
  • Conclusion(s): "It's broken" or "It seems to work"
• Note: The more experiments that succeed, the more confident you are, provided the experiments test different values.
• An additional model from the lab
  • Problem: We have multiple procedures, some of which are likely incorrect.
  • A good test suite should let us identify which are incorrect.
  • Once we've eliminated all of the incorrect ones, we hope to be left with the correct ones.
  • We designed the problem this way to help you think about the kinds of tests you write. If you write a good test suite, you will eliminate most of these procedures.
  • The errors in the various versions are ones we've seen in student code.
• Good testing requires some imaginative thinking: Are there inputs that are different than the ones I've already tried?

A problem in testing

• How can we be confident that a classify-triangle procedure is correct?

• We consider its formal definition.

  ;;; Procedure:
  ;;;   classify-triangle
  ;;; Parameters:
  ;;;   side1, a rational number [unverified]
  ;;;   side2, a rational number [unverified]
  ;;;   side3, a rational number [unverified]
  ;;; Purpose:
  ;;;   Determine the kind of triangle the three sides describe.
  ;;; Produces:
  ;;;   classification, a string 
  ;;; Preconditions:
  ;;;   side1, side2, and side3 together describe a triangle [verified]
  ;;; Postconditions:
  ;;;   If all three sides are equal, classification is "equilateral".
  ;;;   If exactly two sides are equal, classification is "isosceles".
  ;;;   If no two sides are equal, classification is "scalene".
  

• We start with some simple tests.

  (require triangles/tri-0000)
  (define triangle-tests
    (test-suite 
     "Testing classify-triangle"
     (test-case "unit side length equilateral triangle"
                (check-equal? (classify-triangle 1 1 1) "equilateral"))))
  (run-tests triangle-tests)
  

• That's one test. What are some others?

• We should check for isoceles triangles.

     (test-case "simple isosceles triangle"
                (check-equal? (classify-triangle 2 2 3) "isosceles"))
  

• Is that the only way to write an isosceles triangle? Does it matter? Let's try another.

     (test-case "simple isosceles triangle"
                (check-equal? (classify-triangle 2 2 3) "isosceles"))
     (test-case "simple isosceles triangle"
                (check-equal? (classify-triangle 3 2 2) "isosceles"))
  

Improving your tests

• As you write tests, you'll sometimes find that you want to write very similar tests. For example, I might want to try all three isosceles triangles with side lengths 2, 2, and 3 as well as all isosceles triangles with side lengths 10, 10, and 15.

• Rather than copying and pasting the same three lines over and over again, I might write a helper procedure.

  (define isosceles-tests
    (lambda (message same other)
      (test-suite
        message
        (check-equal? (classify-triangle same same other) "isosceles")
        (check-equal? (classify-triangle same other same) "isosceles")
        (check-equal? (classify-triangle other same same) "isosceles"))))
  

• Now in my main suite, I can write

      (isosceles-tests "isosceles: same 2, other 3" 2 3)
      (isosceles-tests "isosceles: same 3, other 2" 3 2)
      (isosceles-tests "isosceles: same 10, other 15" 10 15)
      (isosceles-tests "isosceles: same 1/2, other 1/3" 1/2 1/3)
  

• You'll see this approach on the exam.