Laboratory 14: Unit Testing

Summary: In the laboratory, you will explore the ways in which small tests can help you develop and update code. You will also familiarize yourself with our testing library.

Contents:

• Exercises
  • Exercise 1: Testing the Tester
  • Exercise 2: Testing Triangulation
  • Exercise 3: Writing a Triangle Classifier
  • Exercise 4: A Simple Test Suite
  • Exercise 5: Testing Error Checking
  • Exercise 6: Testing Error Checking, Revisited
  • Exercise 7: Symmetric Tests
  • Exercise 8: Testing Large Sides
  • Exercise 9: Other Tests

Exercises

Exercise 1: Testing the Tester

As you may recall from the reading, unit-test.ss provides four primary procedures:

• (begin-tests!), which prepares the environment for testing.
• (test! expression value), which determines (a) whether expression can be successfully evaluated and, if so, (b) whether the value of expression is value.
• (test-error! expression), which determines whether or not expression reports an error (and treats it as a problem if expression does not).
• (end-tests!), which reports on the tests completed so far.

a. Create a new DrScheme window that will permit you to use unit-test.ss.

b. In the Definitions pane, add the following line and click Run.

(load "/home/davisjan/csc/151/examples/unit-test.ss")

c. In the Interactions pane, try each of the operations a few times to make sure you understand its operation. (Yes, this instruction is intentionally vague.)

d. As you should have observed from your interactions, test! and test-error! give no output. Why do you think the designers made that decision?

e. What happens if you call end-tests! multiple times, perhaps with some intervening calls to test! or test-error! but with no intervening calls to begin-tests!?

Exercise 2: Testing Triangulation

Consider the following procedure documentation:

;;; Procedure:
;;;   classify-triangle
;;; Parameters:
;;;   side1, a real number [unverified]
;;;   side2, a real number [unverified]
;;;   side3, a real number [unverified]
;;; Purpose:
;;;   Determine the kind of triangle the three sides describe.
;;; Produces:
;;;   classification, a symbol 
;;; 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 'isoceles.
;;;   If no two sides are equal, classification is 'scalene.

a. Write a series of tests for this procedure. Your tests should look something like the following:

(load "/home/davisjan/csc/151/examples/unit-test.ss")
(load "/home/rebelsky/Web/Courses/CS151/2006F/Examples/Triangles/tri.0000.ss")
(begin-tests!)
(test! (classify-triangle 1 1 1) 'equilateral)
...
(end-tests!)

b. There are approximately 40 different versions of the procedure of varying degrees of correctness. (Professor Rebelsky wrote a program to create them!) They are named as follows (and all appear in the same directory as tri.0000.ss): tri.0000.ss, tri.0001.ss, tri.0010.ss, tri.0011.ss, tri.0100.ss, tri.0101.ss, tri.0110.ss, tri.0111.ss, tri.0200.ss, tri.0201.ss, tri.0210.ss, tri.0211.ss, tri.1000.ss, tri.1001.ss, tri.1010.ss, tri.1011.ss, tri.1100.ss, tri.1101.ss, tri.1110.ss, tri.1111.ss, tri.1200.ss, tri.1201.ss, tri.1210.ss, tri.1211.ss, tri.2000.ss, tri.2001.ss, tri.2010.ss, tri.2011.ss, tri.2100.ss, tri.2101.ss, tri.2110.ss, tri.2111.ss, tri.2200.ss, tri.2201.ss, tri.2210.ss, and tri.2211.ss

Pick eight or so of those files and run your tests on them. Which ones pass your tests?

Exercise 3: Writing a Triangle Classifier

a. To the best of your ability, write the classify-triangle procedure described in the previous problem.

b. Rerun your tests using this version of the procedure. How many does it pass, how many does it fail? Do not rewrite the procedure to make it pass all these tests.

Exercise 4: A Simple Test Suite

Here is a test that someone might write for the procedure described above.

(load "/home/davisjan/csc/151/examples/unit-test.ss")
(load "/home/davisjan/public_html/csc/151/2006F/examples/triangles/tri.0000.ss")
(begin-tests!)
(test! (classify-triangle 1 1 1) 'equilateral)
(test! (classify-triangle 2 2 3) 'isoceles)
(test! (classify-triangle 3 4 5) 'scalene)
(end-tests!)

a. Does your classify-triangle procedure pass these tests? If not, repair it to ensure that it passes all the tests.

b. Run this test suite on five of the variants mentioned in problem 2 that you have either not tested or that have passed all tests so far. How many pass the new test suite?

c. Can you write an obvious solution to classify-triangle that passes all of these tests, but fails to meet the specifications?

Exercise 5: Testing Error Checking

Someone thinking carefully about the definition of classify-triangle might worry that the tests, as written, do not check for non-triangles. For example, something with side lengths 1, 1, and 3 is not a triangle.

a. Add a test to the testing code above to ensure that classify-triangle rejects that non-triangle.

b. Does your version of classify-triangle pass the revised test suite? If not, correct it so that it does.

c. Run this test suite on five of the variants mentioned in problem 2 that you have either not tested or that have passed all tests so far. How many pass the new test suite?

Exercise 6: Testing Error Checking, Revisited

Another set of inputs for which classify-triangle is supposed to fail is one in which any of the side lengths are negative.

a. Add tests to the test suite for classify-triangle to ensure that classify-triangle rejects any set of three numbers that include a zero or negative number.

b. Does your version of classify-triangle pass the revised test suite? If not, correct it so that it does.

c. Run this test suite on five of the variants mentioned in problem 2 that you have either not tested or that have passed all tests so far. How many pass the new test suite?

Exercise 7: Symmetric Tests

We've tested for each of the three kinds of triangles, but we've only one test for each. What if the programmer mistakenly forgets to deal with the different orderings of parameters? We should make sure that the implementation works for each.

a. Add tests to the test suite for classify-triangle to ensure that classify-triangle correctly identifies the three kinds of triangles, not matter what the ordering. In particular, make sure that you test for the three variants of isoceles triangles.

(test! (classify-triangle 2 2 3) 'isoceles)
(test! (classify-triangle 2 3 2) 'isoceles)
(test! (classify-triangle 3 2 2) 'isoceles)

b. Are there other tests in which the ordering might matter? (Hint: Think about some of the tests for errors.)

c. Does your version of classify-triangle pass the revised test suite? If not, correct it so that it does.

d. Run this test suite on five of the variants mentioned in problem 2 that you have either not tested or that have passed all tests so far. How many pass the new test suite?

Exercise 8: Testing Large Sides

We now might consider the range of side values for which classify-triangle should be tested. In the past, we've seen that eq? doesn't consider large numbers equal, even when = and eqv? do. So, let's add some tests.

a. Add tests that ensure that classify-triangle works for very large numbers (say, numbers greater than 10 billion).

b. Does your version of classify-triangle pass the revised test suite? If not, correct it so that it does.

c. Run this test suite on five of the variants mentioned in problem 2 that you have either not tested or that have passed all tests so far. How many pass the new test suite?

Exercise 9: Other Tests

a. Add any other tests you conceive of (and be prepared to discuss those tests in class).

b. Does your version of classify-triangle pass the revised test suite? If not, correct it so that it does.

c. Run these tests on any variants mentioned in problem 2 that you have not yet tested or that have passed all the tests up through exercise 9. How many pass the tests?

Janet Davis (davisjan@cs.grinnell.edu)