Hacker News Reader

Comment by nickbarnwell | Hacker News Reader

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#?

View on HN

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/

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!

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.

Reply on news.ycombinator.com