Research: Contract Checking and Automated Test Generation with Pex
- Posted: Oct 29, 2008 at 9:39 AM
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- 11 Comments
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In theory, Design by Contract and unit testing are excellent approaches to improve code quality. Learn how to use code contracts that express pre-conditions, post-conditions, and object invariants in any managed language that improve testability, enhance
static analysis, and serve as checked API documentation. Contracts are leveraged for advanced static analysis and translated into runtime checks. See how automated program exploration (Pex) discovers boundary conditions in code that cause failures and generates
traditional unit test suites with high code coverage. Contracts and Pex work together to target contract checks, runtime failures (null dereferences, index out of range, etc.), and any other kind of assertions. Use them to write higher quality software with
less effort.
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Nikolai TillmannNikolai Tillmann has been with Microsoft Research for 6 years. He is currently leading the Pex project, building an automated test case generation tool for .NET based program analysis. Previously, he worked on Spec Explorer, a model-based testing tool.
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Mike BarnettMike Barnett has been at Microsoft Research since 1995. He has spent the last several years working on the Spec# project, an advanced verification environment and language for .NET.
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Great stuff!
I must admit I was saddened to hear Spec# wouldn't be integrated into C# 4. But this is the next best thing; I'm glad to see design-by-contract getting some attention in the .NET framework itself.
If I may comment on the presentation, it feels like you both should have had your own presentations. It felt too rushed and too crammed.
Having Mike go deeper into the evolution of Spec# and why they chose a library instead of C# langauge integration would've been great. And Nikolai covering more real-world unit testing scenarios with Pex - for example, testing code with dependencies like the file system or UI using Pex, would have been a great presentation by itself.
Also, the rehearsed Q&A between Mike and Nikolai was cheesy. Too tongue-in-cheek!
Beyond that, great stuff guys! I'm really happy to see DbC getting some real attention, I believe it will help us write code that more clearly expresses our intent and contains fewer bugs. That's something every developer can get behind. Going to go download and play with the VS2008-integration...
I'd like to give you guys some feedback as I considered how we would integrate this stuff into our codebase (that is, once contracts are under a commercial-friendly license!). Where do we send feedback?
Cheers,
Justin Van Patten
Program Manager
Common Language Runtime
But until this stuff is released under a non-research license, I just can't feel like I can use it and invest any time into it
But great talk, great work on the technology...these are the things that excite me about where Microsoft is going
I just wanted to point out that we have a web site for the project: http://research.microsoft.com/contracts. That page contains a link to an email alias we've set up: codconfb _at_ microsoft _dot_ com. You can use that to send specific comments about the tools and the many bugs I'm sure you'll find in our tools. The alias is unfortunately one-way. We can see the mail you send to it, but you can't join the alias. We are working on a separate forum for the Code Contracts project, but it isn't set up yet.
Mike
In the talk you mention that you do IL-weaving to inject the right code for the contracts. Is this IL reader/writer something that can be used separately from Contracts? I've been using Cecil (http://www.mono-project.com/cecil) for some R&D stuff and it would be awesome if there was something like this somewhere from Microsoft
Regards,
Jason
Pex is now available for Visual Studio 2008 under the pre-release license. Check it out at http://research.microsoft.com/pex/downloads.aspx .
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