This post is specific to the Code Digger Add-In, which can be used with Visual Studio 2012 and 2013.

Requirements

• Download the Microsoft Code Digger add-in

This will appear in Tools | Extensions and Updates and ofcourse can be downloaded via this dialog.

What is Pex ?

So Pex is a tool for automatically generating test suites. Pex will generate input-output values for your methods by analysing the flow etc. and arguments required by the method.

What is Code Digger ?

Code Digger supplies an add-in for Visual Studio which allows us to select a method and generate input/outputs using Plex and display the results within Visual Studio.

Let’s use Code Digger

Enough talk, let’s write some code and try it out.

Create a new solution, I’m going to create a “standard” class library project. Older versions of Code Digger only worked with PCL’s but now (I’m using 0.95.4) you can go to Tools | Options in Visual Studio, select Pex’s General option and change DisableCodeDiggerPortableClassLibraryRestriction to True (if it’s not already set to this) and run Pex against non-PCL code.

Let’s start with a very simple class and a few methods

public static class Statistics
{
   public static double Mean(double[] values)
   {
      return values.Average();
   }

   public static double Median(double[] values)
   {
      Array.Sort(values);

      int mid = values.Length / 2;
      return (values.Length % 2 == 0) ?
         (values[mid - 1] + values[mid]) / 2 :
         values[mid];
   }

   public static double[] Mode(double[] values)
   {
      var grouped = values.GroupBy(v => v).OrderBy(g => g.Count());
      int max = grouped.Max(g => g.Count());
			
      return (max <= 1) ?
         new double[0] :
         grouped.Where(g => g.Count() == max).Select(g => g.Key).ToArray();
      }
   }
}

Now you may have noticed we do not check for the “values” array being null or empty. This is on purpose, to demonstrate Pex detecting possible failures.

Now, we’ll use the Code Digger add-in.

Right mouse click on a method, let’s take the Mean method to begin with, and select Generate Inputs / Outputs Table. Pex will run and create a list of inputs and outputs. In my code for Mean, I get two failures. Pex has executed my method with a null input and an empty array, both cases are not handled (as mentioned previously) by my Mean code.

If you now try the other methods you should see more similar failures but hopefully more successes with more input values.

Unfortunately (at the time of writing at least) there doesn’t appear to be an option in Code Digger to generate either unit tests automatically or save the inputs for my own unit tests. So for now you’ll have to manually write your tests with the failing inputs and implement code to make those work.

Note: I did find at one time the Generate Inputs / Outputs Table menu option missing, I disable and re-enabled the Code Digger Add-In and restarted Visual Studio and it reappeared.