Overview

• Preliminaries.
• An introduction to testing.
• An introduction to unit testing.
• Thinking about unit testing in C.
• Exercise, part 1: Write binary search.
• Exercise, part 2: Test binary search.

Preliminaries

Homework

• Think about how you would test binary search!

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Questions

An introduction to testing

• We have a responsibility to write correct software (or at least do our best to write correct software).
• Gold standard: Formal proof.
  • Difficult
  • Error prone
• Experimentation / testing
• Good programmers test
• Better programmers write tests before they write code
  • Less bias from/toward the code you write
  • Helps you think more carefully about the code you're going to write.
  • Make programming a (really bad) video game: "Look, I'm down to 10 failed tests". "Measurable" evidence of progress.
  • Tests document.

An introduction to unit testing

• Test smaller units of the program individually
• Test using a framework in which you get a report of either "all tests successful" or failures. (The computer, rather than a human, makes sure that the output of each procedure is right.)
• Modern languages include test frameworks - Java - JUnit
• There is no standard for C.

What do we do when we have to unit test our C programs? (You want the computer to read the output!)

• Write code by hand

  if (fun(input) != expected_value)
    fprintf (stderr, "Test case 43.1 failed!");
  

• Write an interactive tester (tester)

  • Write a textual input file, (inputs)
  • Write a list of expected outpus (outputs)
  • `tester < inputs > new-outputs; diff outputs new-output"

• Write a generalized testing framework. (Using Macros?)

• Find an existing testing framework. Just because there's no standard, it doesn't mean there isn't one.

  • Variant: Stackoverflow "My annoying CS Prof expects us to do unit testing in C. What would you recommend, other than switching classes?"
  • Note: A good testing framework influences how you test.

• Tradition in C: Use assert

Exercise, part 1: Write binary search

/home/rebelsky/Web/Courses/CSC282/2015S/examples/binary-search
<http://www.cs.grinnell.edu/~rebesky/Courses/CSC282/2015S/examples/binary-search>

Exercise, part 2: Test binary search