CSC 207.02 2019S, Class 05: Unit testing and debugging

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• Quiz
• Testing lab
• Debugging lab

Preliminaries

News / Etc.

• Mentor sessions at 7:00 p.m. Sunday nights.
• Ramadan begins during Week 14 this semester. I will do my best to make appropriate accommodations during week 14 and finals week. College policy suggests that you must notify me by the end of this week if you need such accomodations, but I will make them no matter when you notify me.
• The “Current Writeup” link should now be working.
• I graded any lab 4’s I received by 7pm Sunday night. Make sure you let me know if you know you’re submitting non-working code on labs.
• To make sure that you have enough time for lab, I’ll try to avoid much talking today.
• JUnit’s API changed significantly from JUnit4 to JUnit5. I think I’ve caught all of the code that needed changing, but there may be a few left.
• Due to a confluence of circumstances, it appears we will have few MAPs in the department this summer. Check with JW and CC for details on their MAPs.

Upcoming work

• Assignment 2 due Thursday night.
• Reading due before class Wednesday
  • Osera 3.1: Mental Models of Computation
• Lab writeup: Problem 1 from the Debugging Lab
  • To csc207-01-grader@grinnell.edu
  • Subject: CSC 207.01 Writeup for Class 5 (Your names)
  • Submit the corrected code for the removeAs method.

Extra credit

Extra credit (Academic/Artistic)

• CS Table, Tuesday, Noon, CS Commons: Machine learning and criminal justice.
  • Simonite, Tom (2017). How to upgrade judges with machine learning.
    MIT Technology Review. https://www.technologyreview.com/s/603763/how-to-upgrade-judges-with-machine-learning/
  • Angwin, Julia, Larson, Jeff, Mattu Surya, and Kirchner, Lauren.
    Machine bias. Pro Publica. https://www.propublica.org/article/machine-bias-risk-assessments-in-criminal-sentencing
• CS department advising forum, Thursday, 11am.
• Once Upon a Time Wolf (tickets required), Bucksbaum. Friday, 8 February, 7pm.
• Once Upon a Time Wolf (tickets required), Bucksbaum. Saturday, 9 February, 7pm
• HackGC
• Ilovedataweektoo

Extra credit (Peer)

• Home track meet, 10am-6pm Saturday (30 min counts)

Extra credit (Wellness)

• HIIT training, 4:30 pm, Tuesday, Dance Studio, Bear. (Cap of two EC units.)
• Hatha Yoga, 7:00 pm, Tuesday, Dance Studo, Bear. (Cap of two EC units.)
• Sex Week events.

Extra credit (Misc)

• Leadership Institute info session, Tuesday, 7 p.m. JRC 2nd.

Other good things

Questions

Should our repos be public or private?

Private.

Does our program have to close the drawing panel, or should we make the user do so?

Either.

What is agile software development?

A “new” methodology for developing software, based on the idea that client expectations change regularly, we adapt to those changes. Lots of practices, including pair programming, test-driven-development, “stand ups”, refactoring, … (We use it in 324.)

Tell me more about static functions

“Normal” (object) functions are associated with individual objects.

    Thingy t = new Thingy(...);
    t.explode();

Some functions shouldn’t need objects. We name these “static” functions. We notate them with the static keyword. We call this ClassName.function()

    public class Helpers {
      /**
       * Convert from centigrade to fahrenheit ...
       */
      public static int c2f(int f) {
        ...
      }
    } // class Helpers

    ...
    pen.println("If it's 32 degrees centigrade, it's " + Helpers.c2f(32)
                + " fahrenheit.");

It’s a lot like the procedures we learned in C, with the difference that we put them in classes rather than libraries.. (And we write static)

Are fields accessible to static methods?

No. Not even the main method.

(Static fields are accessible to static methods.)

What about private fields?

Only accessible to objects in that class.

Can I ask a followup question?

Yes

Since c2f is public, I can access it anywhere, right?

More or less.

Must main be static?

Yes.

Lab: Testing

So that we have enough time for the debugging lab, read, but do not do, exercise 4 of the testing lab.

What do you expect as output for the following program?

public class Experiment {
  public static void main(String[] args) {
    System.out.println(9/5);
  } // main
} // class Experiment

What’s wrong with c2f?

• The formula is backwards.
• Integer division!

What should we take from the sum example?

• Good pre/posts are hard, particularly in languages with fixed precision.
• Designing tests requires some thought.

What should we take from the expt example?

• There’s a divide-and-conquer way to do exponentiation that is significantly faster.
• Tests with double values are a bit more complicated.
• Loops help you do more comprehensive tests.

Lab: Debugging

Writeup: Exercise 1 from Debugging lab

• To csc207-01-grader@grinnell.edu
• Subject: CSC 207.01 Writeup for Class 5 (Your names)
• Submit code for removeAs