Pex is a tool from Microsoft Research that aims to automate unit testing by generating test inputs through static and dynamic analysis of code. It learns more about the code over time to generate inputs that increase code coverage. Pex has been used internally at Microsoft to test core components and is available today for Visual Studio 2008 and 2010, though it has some limitations as a research project. The document discusses Pex's capabilities, examples of its use, and its potential future applications when combined with techniques like behavior-driven development and code contracts.

1. Pex
The future of unit testing?
Ben Hall
Ben@BenHall.me.uk
Blog.BenHall.me.uk

2. Agenda
• What is Pex?
• Problem Pex is trying to solve
• Pex in the Real World
• The future?

3. What is Pex?

4. Program Exploration

5. Microsoft Research
Research in Software Engineering
(RiSE)

6. Nikolai Tillmann
Peli de Halleux
Wolfram Schulte
Nikolaj Bjørner

7. Nikolai Tillmann
Peli de Halleux
Wolfram Schulte
Nikolaj Bjørner

8. Pex generates inputs for your unit
tests through automate exploratory
testing

9. Identify Test Inputs
• Pex doesn’t make wild guesses
• Pex gains an understanding of your code
• Static and dynamic analysis
• Every input should increase code coverage

10. Parameterised Unit Tests
[RowTest]
[Row(1, 2, 3)]
[Row(-1, -2, -3)]
public void TestForAddMethod(int a, int b, int
expected)
{
int test = MyMethods.Add(a, b);
Assert.AreEqual(test, expected);
}

11. Parameterised Unit Tests
[RowTest]
[Row(1, 2, 3)]
[Row(-1, -2, -3)]
public void TestForAddMethod(int a, int b, int
expected)
{
int test = MyMethods.Add(a, b);
Assert.AreEqual(test, expected);
}

12. Everything Ian said is still valid

13. Exploratory Testing
• Learns more over time
• More it knows, more it knows how to break it
• Starts with simplest input

14. DEMO
HELLO WORLD

15. Under the covers

16. CLR Profiler API
ICorProfilerCallback2

18. Z3 Constraint Solver

19. The Problem

20. Some people aren’t unit testing
Ok... Most people

21. Lots of people think they are
writing tests but in reality they
aren’t

22. [Test]
public void Test1()
{
Engine e = new Engine();
Customer c = e.GetCustomer(123);
Order o = new Order(1, “Product X”)
o.Customer = c;
Assert.IsTrue(e.PlaceOrder(o));
}

23. Those who are, 100% code
coverage is rare
Especially with Legacy Code

24. Test Driven Development on
complex code is difficult

25. Encryption and Decryption
algorithms

26. Parsers and Compilers

27. Decision Tables

28. Aim of Pex is to solve these
problems

29. The Real World

30. DEMO
DECISION TABLE

31. DEMO
IP ADDRESS GENERATOR

33. DEMO
PEX EXTENSIONS

34. The Future

35. Pex has limitations
Remember – it’s still research

36. Difficult to start using
Remember – it’s still research

37. Not available under a
commercial license
VS2008 == Research
VS2010 == Same as VS2010 CTP

38. However!

39. Very good with algorithms and
complex code

40. Used internally to test core
component at Microsoft

41. Code Contracts help guide Pex
Spec# C# 4.0

42. BDD and Pex

43. In summary...

44. Summary
• Pex is a project from Microsoft research
• Available today for VS2008 and VS2010
• Aims to make unit testing more effective
• BDD + Pex

47. Thank you
Ben Hall
Ben@BenHall.me.uk
Blog.BenHall.me.uk

48. Resources
• http://Blog.BenHall.me.uk
• http://research.microsoft.com/pex/
• http://www.codeplex.com/pex
• http://blog.dotnetwiki.org/ (Peli’s Blog)
• http://blogs.msdn.com/nikolait
• PDC Session -
http://channel9.msdn.com/pdc2008/TL51

49. Flickr Images
• http://www.flickr.com/photos/djbrady/1460272108/
• http://www.flickr.com/photos/yukonblizzard/2562986
305/
• http://www.flickr.com/photos/frielp/6829509/
• http://www.flickr.com/photos/atomicjeep/274667176/
• http://www.flickr.com/photos/wouterpostma/6958502
12/
• http://www.flickr.com/photos/leon_homan/28566287
78/
• http://www.flickr.com/photos/sadsnaps/2741479621/