1. Dynamic Symbolic Execution
Tao Xie

2. Test Data Generation Human Brute Force Semi - Random
Expensive, incomplete, …
Brute Force
Pairwise, predefined data, etc…
Semi - Random
Cheap, Fast
“It passed a thousand tests” feeling
Dynamic Symbolic Execution: IntelliTest/Pex, SAGE, CUTE, …
Automated white-box
Not random – Constraint Solving

3. Assumptions and Assertions
void PexAssume.IsTrue(bool c) { if (!c) throw new AssumptionViolationException(); } void PexAssert.IsTrue(bool c) { if (!c) throw new AssertionViolationException(); }
Assumptions and assertions induce branches
Executions which cause assumption violations are ignored, not reported as errors or test cases

4. Background: DSE Choose next path Generates test data systematically
Solve
Execute&Monitor
void CoverMe(int[] a) {
if (a == null) return;
if (a.Length > 0)
if (a[0] == )
throw new Exception("bug"); }
Constraints to solve
a!=null
a!=null &&
a.Length>0
a.Length>0 &&
a[0]==
Input
null {}
{0}
{123…}
Observed constraints
a==null
a!=null &&
!(a.Length>0)
a==null &&
a.Length>0 &&
a[0]!=
a[0]==
a==null F T
a.Length>0 F T
Done: There is no path left.
a[0]==123… F T 4 4 4 4

5. Pex4Fun 1,857,924 clicked 'Ask Pex!' http://pex4fun.com/
Nikolai Tillmann, Jonathan De Halleux, Tao Xie, Sumit Gulwani and Judith Bishop. Teaching and Learning Programming and Software Engineering via Interactive Gaming. In ICSE 2013, SEE.

6. Pex4Fun https://sites.google.com/site/teachpex/Home/pex-usage-tips
Click 
Copy and modify the following code snippet in the code editing box (or simply click here)
using System; using Microsoft.Pex.Framework; using Microsoft.Pex.Framework.Settings;
[PexClass] public class Program  {
[PexMethod]//[PexMethod(TestEmissionFilter=PexTestEmissionFilter.All)]   public static string testMethod(int x, int y)   {
    PexAssume.IsTrue(y >= 0);//replace here with your assumption     //... enter your code under test here     //if (x == 10000) throw new Exception();
    PexAssert.IsTrue(y >= 0);//replace here with your assertion     return PexSymbolicValue.GetPathConditionString();   } }

7. Microsoft Visual Studio 2015/2017 IntelliTest

8. Microsoft Visual Studio 2015/2017 IntelliTest