Overview

• Preliminaries
  • Admin.
  • Homework questions.
• A few remaining notes on Git.
• A few notes on unit testing.
• An example: Testing exponentiation.
• A few notes on test-driven development.
• Lab!

Admin

• What should earnestw do about his gmail account?
  • Write a custom spam filter
• I made some changes to the CSS stylesheet for the class. Let me know if you notice and whether the changes are an improvement or (whatever the opposite of improvement is).
• A friendly reminder that "Learning from Alumni" is a great opportunity to get real-world recommendations on how to prepare for a job or internship (and to network). And you get 1 credit. Thursdays, 2:15-4:05.
• Reading for Monday: Debugging
• I'm working on getting more of the assessment forms up. Sorry for the delay. (My primary goal is making sure that the readings and labs are up to snuff.)
• EC opportunities:
  • CS Table, today,! Alan Turing on AI.
  • Humanties Center Speaker Sarah Hendron, Next Wednesday, 7:30 p.m., JRC101 Waking the Machines: Art, Design, and Adaptive Technology
  • Learning from Alumni 2:15-4:05 next Thursday: Ian Lunderskov '08
  • Tentative Thursday Extra next week: Matt Atherton '95
• Mentoring is Wednesday nights at 8-9pm

Questions on HW2

• Does anyone need a partner for HW2?
• Are there questions on HW2? I see only two of you have filled out the prologue, which suggests few people have looked at the homework.
• Question: Can I really write "isOdd" without using %, /, *
  • Yes, if you are willing to interpret the assignment in a certain way.
  • Yes, if you are willing to write ugly and inefficient code?

A few remaining notes on Git

• There are GUI's for command-line git
  • GitHub for Mac is really good (So says Sunny Shine)
• git commit -m "*Message*" provides a faster way to commit.

A few notes on unit testing

• One strategy for seeing if your code works: Call the procedure, print out the result
• Why that strategy is bad
  • You have to spend time comparing results - Computers are faster
  • You have to remember what result you expected (you probably have to document)
  • You won't want to do many tests
• What's the solution? A test framework
  • You write the tests as code that specifies input and expected output
  • The computer does all the work
  • Rerunning the tests is easy
  • And you can write loops to generate lots of tests
• We'll call this strategy "unit testing" -
• Designing good tests requires practice and thought
• And a testing framework
  • We'll use JUnit

An example: Testing exponentiation

    /**
     * Compute x^n
     * @pre
     *   x^n < Integer.MAX_VALUE
     *   x^n > Integer.MIN_VALUE
     */
     int expt(int x, int n)

• One test: 9 == expt(3,2)

  assertEquals("D's Test", 9, expt(3,2));
  

• Another test: 1 == expt(posint,0)

    for (int i = 0; i < 10000; i++) {
      assertEquals(i + "^0", 1, expt(i,0));
  } // for
  

• Negative tests

  assertEquals("Negative", 1, expt(-2,0));
  assertEquals("Negative", -2, expt(-2,1));
  assertEquals("Negative", 4, expt(-2,2));
  assertEquals("Negative", -8, expt(-2,3));
  

• A for loop to do a lot of tests

  for (int base = 2; base < 500; base++) {
       assertEquals(base + " squared", base*base, expt(base, 2));
       assertEquals(base + " cubed", base*base*base, expt(base, 3));
  } // for
  

• A for loop for a power of 1

• Detour: Java specifies that integers are 32 bits, excess 2^m-1 notation 32 bits: If only positive, largest 2^32-1; if you allow negative, it's even smaller (maybe 2^31-1, if I remember the notation)

• Nest for loops: Different bases, different powers

  for (int power = 1; power < 6; power++) {
      assertEquals(3 + "^" + power, ...,expt (3, power)); 
  } // for
  

• Something complicated that lets us get back to the original number

A few notes on test-driven development

Skipped

Lab!

Insufficient time. Finish up on your own.