Microsoft Code Digger

http://channel9.msdn.com/coding4fun/blog/Digging-into-your-code-with-the-free-Microsoft-Code-Digger-and-the-power-of-Pex

by scottcha • 13 years ago

137 23 13 years ago

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testbro• 13 years ago

A similar tool exists for Java, although it doesn't rely on symbolic execution (but IIRC it is able to use it for integer constraints) but evolutionary test data generation [1]. There's a plugin for Eclipse too.

[1] http://www.evosuite.org

nickbarnwell• 13 years ago

I'll prefix my question by saying I'm unfamiliar with QC beyond knowing of its existence and roughly what it does in terms of generating test values:

Am I misunderstanding, or is this akin to QuickCheck for C#?

danbruc6• 13 years ago

The QuickCheck manual states that they are randomly generating test cases [1]. This tool is build on top of Pex [2] which analyzes the byte code and uses the Z3 theorem prover [3] to systematically find inputs covering all code paths. This is really a impressive and powerful tool. You can have some fun with it at the Pex for fun site [4]. There is some secret code and you have to reimplement that code based on the test results generated by Pex comparing your implementation to the secret implementation.

[1] http://www.cse.chalmers.se/~rjmh/QuickCheck/manual.html [2] http://research.microsoft.com/en-us/projects/pex/ [3] http://research.microsoft.com/en-us/projects/z3m/ [4] http://www.pexforfun.com/

0x0• 13 years ago

The pexforfun thing seemed pretty clever:

  // What values of v and i can cause an exception? Ask Pex to find out!
  public static void Puzzle(int[] v, int i)
  {
    if (v[i + 2] + 5 == v.Length + i)
      throw new Exception("hidden bug!"); 
  }

and then it automatically finds the breaking input:

  {-6} 	 -2 	 Exception 	 hidden bug!

porges2• 13 years ago

It's better than QuickCheck. It performs whitebox testing - that is, it has knowledge of the code and actively uses this to generate inputs that explore all possible branches.

earlz• 13 years ago

I tried it. Doesn't usually work all that well though, and basically only works on built in .Net types. If you pass in your own object containing only .Net types, it's not smart enough to fill those in with potential test data. Interesting idea, but I found it completely worthless

danbruc6• 13 years ago

I can not test it at the moment but you may have to do the object creation inside a wrapper method.

  public static void TestWrapper(String foo, Int32 bar, Boolean buzz, Decimal foobar)
  {
     var thing = new Thing(foo, bar);

     thing.Buzz = buzz;

     Test(thing, blah);
  }

  public static Test(Thing thing, Decimal foobar)
  {
     thing.DoStuff();

     if (thing.State == 42)
     {
        thing.DoOtherStuff(foobar);
     }
  }

In my experience Pex yields really great results when you use it to analyze methods that are close to mathematically functions with not to many side effects and especially state mutation. Tracking changing state over time and finding sequences of operations to prepare an object to a certain state and then checking the behavior of the object in this state is much harder than analyzing a (almost) pure function.

georgefox• 13 years ago

You can test it online at pex4fun.com. Here are two tests, one using a function that takes built-in types as parameters and instantiates a Thing to operate on, and a second that takes a Thing input and operates on it directly. It seems to generate interesting cases for both, but it's much more easily readable with the more basic input types, as the parameters are easily displayed in the table.

http://pex4fun.com/default.aspx?language=CSharp&code=OgP...

http://pex4fun.com/default.aspx?language=CSharp&code=_QL...

romaniv• 13 years ago

It would be very, very useful if only it worked with regular expressions. Or if you could run it against F# functions.

porges2• 13 years ago

Rex is the equivalent of Pex (which is what this is based upon) for regular expressions: http://research.microsoft.com/en-us/projects/rex/

danbruc6• 13 years ago

I just tested it using Pex for fun and - to my surprise - Pex was able to deal with regular expression and this AFAIK without any build-in knowledge of regular expressions.

  using System;
  using System.Text.RegularExpressions;

  public class Program
  {
    public static String Puzzle(String input)
    {
      if (new Regex("123(foo|bar){3}456[0-9]{5}789").IsMatch(input))
      {
        throw new ArgumentException();
      }
      else
      {
        return input;
      }
    }
  }

Pex reported three test cases.

  null                         ArgumentNullException
  ""                           okay
  "123foobarbar45600000789bb"  ArgumentException

Try this example yourself.

http://www.pexforfun.com/default.aspx?language=CSharp&co...

UPDATE: I was wrong - Rex was integrated into Pex in 2010 and this made Pex much smarter when it has to deal with regular expressions.

SanjayUttam• 13 years ago

And more useful still if this worked on more than just portable class libraries [like the "original" Pex]

Aurel1us• 13 years ago

Anyone know something similar for C/C++ or Python ?

monksy• 13 years ago

Or for Java.

danbruc6• 13 years ago

https://news.ycombinator.com/item?id=5676010

grdvnl2• 13 years ago

Pex is based on the Daikon dynamic invariant. This document explains some results and examples in certain languages.

http://groups.csail.mit.edu/pag/daikon/download/doc/daikon.p...

judah• 13 years ago

It's based on the Z3 solver, here's Z3Py: http://rise4fun.com/z3py

Yuioup• 13 years ago

I've noticed here and on reddit that Microsoft stories don't get much attention. Rightly so?

suyash• 13 years ago

Anything similar for JavaScript?

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