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Sunday, August 29, 2010

Code Anthem: What Can Change

Friday night I wrote an introduction to a site called Code Anthem, which tests the skills of a programmer and uses those results to help employers find talented individuals. As I said then, I think the idea is a pretty awesome one, and I think it has a lot of potential to help employers with the tricky technical screens that so many companies get wrong.

Today I'm going to talk a little bit about what I think Code Anthem can do differently, and how they can grow the service into something that would have real, industry-wide value.

The tests at Code Anthem tend to focus pretty narrowly on algorithms: Determine whether one array is a subset of another array, Determine if a string is a palindrome, Calculate the perimeter of a polygon, Validate a password. These are all relatively simple things and once you know the necessary algorithm it tends to be a simple matter of translating it into the target language. With a little bit of a brush up for me to re-familiarize myself with the core classes and methods, I could probably do as well in the Java test as I did in the C# test, and I absolutely would not consider my mad Java skillz to be at the same level that my C# abilities are. I was decent with the language in college when I was using it, but skills do fade if you don't use them and I have certainly not been using Java.

A test for problem-solving and basic language syntax tests exactly that: problem solving and basic language syntax.  One question involved calculating the Fibonacci sequence, and while my solution was pretty efficient, I could easily have used the classic, naive recursive implementation and thrown performance considerations to the wind. Would this provide me the correct answers to test input? yes. Would this be an acceptable answer? Absolutely not. So, testing that I can solve a problem which has several known solution algorithms doesn't necessarily mean that I will pick a good one, and doesn't necessarily mean that I've solved the problem well.

Looking at this another way, I know that the recursive solution (which is perfectly acceptable input) starts to go hell-crazy above a certain input level. Assuming that Code Anthem isn't evaluating solutions on a supercomputer at the NSA, it's pretty reasonable to assume that they aren't going to be testing the solution with inputs above 30ish, and absolutely no inputs above 45. With this devious knowledge in mind, I don't need an algorithmic solution at all, all I need to do is provide an answer that must work for the set of inputs that they can reasonably use to test:

int fib(int idx) {
return (new int[] {1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...})[idx - 1];

Again, not an acceptable solution to the problem under any circumstances, but it does work and it does require a little bit more insight than the recursive solution does.

Any programmer who really thinks that the naive recursive solution to the Fibonacci problem is an acceptable one really should fail the test no matter how accurate the results are. It may be technically correct, but it is an example of extremely poor problem solving, lazy coding, and a complete disregard for real-world performance issues. It would be relatively trivial to run tests in a sandbox thread with a timed kill-switch: If the timer goes off before a solution is found, the complexity must have been too high and the result is failure.

I've digressed a little bit: If you're only testing problem-solving and an ability to dump a solution from your brain into the syntax of the target language, you're not testing much. I've known a lot of really lousy programmers who would be able to solve many of these problems, even if the quality of the final solution was severely lacking.

When I taught Embedded C coding in college, I used to hear from students all the time that their grades should have been higher because "it compiles", and somehow that always seems good enough. The reality is that compilation is the milestone that separates a file of source code from a file of unintelligible gibberish. Just compiling means that what you wrote is software, but not that it's correct, robust, maintainable, or even acceptable. To earn these other distinctions, more work above simply getting the syntax right is required. In the Code Anthem test, they're testing a slightly higher level, but not by much. Yes they can show that the code compiles and that it correctly produces the correct results, but they cannot show that the code is "good" nor that the programmer is "competent", or "capable" or "worth hiring".

C# is a pretty rich language, even if you stick with the popular 3.5 version and not the new 4.0. Of course, 4.0 doesn't add a whole hell of a lot to the core language, so we can really ignore it for now. Features like contravariance of generic types are certainly nice, but the new version doesn't have huge market penetration yet so we can't expect most people to know about it. Testing for a basic ability to write functions and loops, and a basic understanding of core types really misses out on many of the important features of C#, and really does nothing to separate the coders who don't know the language well from those that do.

A C# or Java test which does nothing to test knowledge of object-oriented concepts, such as classes and inheritance, really isn't a comprehensive test of those languages. If you can't use inheritance, don't understand the difference between is-a and has-a relationships, and don't know what keywords like "interface", "abstract" and "virtual" do, you really don't know C#.

In C#, if you don't understand delegates, you could get in trouble pretty quickly. Understanding the difference between a method group identifier and a delegate can be a simple and confusing mistake for inexperienced programmers. Not understanding the difference between normal and multicast delegates can lead to some very weird runtime effects. Not understanding anonymous delegates, closures, and dynamic invocation really can really separate out the entry-level C# coders from from the advanced programmers and gurus.

Beginner C# coders will know the basics about syntax: classes, functions, loops, variables, operators. Median C# coders will be using interfaces, inheritance, delegates, exceptions, and built-in generics. Good C# coders will  be doing all the previous things correctly and at a higher level, plus mixing and matching all these tools and techniques to solve complex problems.

All of the tests in Code Anthem (at least those that I saw) gave the test-taker a function prototype and some instructions, and asked for the body of the function to be filled in. A different, more comprehensive type of problem would give an interface definition and ask the user to implement an entire class. An extremely comprehensive test would present many types of questions:

  1. Implement a function to have a particular behavior, given a signature and a description.
  2. Implement a class to provide a specific interface, given the interface and a description of behavior.
  3. Given a piece of pre-written code with bugs, identify and fix the bugs.
  4. Multiple choice questions about language features which would be hard to test practically.
You'd probably want to put some kind of time limit on those multiple choice questions, but there are some things that you're not going to really be able to test without them.

There are plenty of ways to run this kind of a test. You could do it like a game show, such as "Who wants to be a Millionaire": People start with a score of zero, and gradually move up the scale as they answer ever harder and harder questions. The really good ones might have to spend some time on the test, so it would be good to break it up into stages that can be tackled at different times.

Another option would be to break up the test into several smaller tests focusing on different issues. Some tests could even be language-agnostic, such as figuring out how to solve particular problems where language-specific syntax or semantics doesn't play much of a role in the solution.

What Code Anthem does now is a basic test to weed the programming bozos from non-bozos. This is certainly a good first step, but really doesn't do anything to differentiate between the coders who are good at what they do from the true creme de la creme of potential applicants (and everybody in between). Weeding out the obvious bozos is still a good service to render, but it really falls short of a potential that a system like this has.

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