Software quality with Code Contracts and PEX - CodeCamp16oct2010

Software quality with Code Contracts and PEX
SorinDAMIAN

Contracts
Design by Contract ™
Code contracts and runtime checking (Foxtrot)
Static verification (Clousot)
Documentation
Automated unit testing (PEX)

Design by contract
Described in articles since 1986
Around since the Eiffel language
Bertand Meyer
Analogy with business contracts
Contracts
Preconditions (What does the method expect?)
Postconditions (What does it guarantee?)
Invariants (What does it maintain?)

Microsoft Code Contracts Library
Microsoft Research
Code contracts and runtime checking (Foxtrot)
Static checker (Clousot)
Available for .NET 2.0 as an external assembly
Included in .NET 4.0
Integration with Visual Studio 2008/2010
Available in all .NET programming languages

Microsoft Code Contracts Tools
Runtime checking
ccrewrite.exe
Static program verification
cccheck.exe
Documentation generation
ccdoc.exe
Automatic testing tools like PEX can take advantage of contracts

Expressing contracts
Requirement and specification documents
Code comments
Guards / defensive programming
CodeContracts
Contract.Requires(arg != null);
Contract.Ensures(Contract.Result<int>() > 0);
Contract.Invariant(this.Total > 0);
Assertions
Assumptions

Code Contracts
Contracts vs. Validation
Handling legacy code
Pre and post conditions
Documentation
Handling contract failures
Contract violation events
Assert on contract failure
Contracts on interfaces and base classes
Contracts inheritance
Adding contracts to external libraries
Contract reference assemblies
Using a baseline for large projects

Demo
using System.Diagnostics.Contracts;

Code Contracts
Preconditions
Legacy contracts
Post conditions
Invariants
Side effects and pure methods

Demo
Interfaces and contracts inheritance

Known issues
Build slowdown due to the assembly rewriter
No mechanism to provide contracts on delegates
Static checker doesn’t work with closures and yield iterators
You may get static checker errors for generated code
No edit and continue support

Static verification
Floyd-Hoare logic proposed in 1969
Sir Charles Antony Richard Hoare
Design by Contract
Bertrand Meyer
Spec#
Microsoft Research (credits go here..)
Code contracts library in .NET Framework 4.0

Static verification
Verification vs. Testing
Abstract interpretation
Working with existing projects

Pex Explorer

Pex Explorer
Automated white box testing tool for .NET
Parameterized unit tests
Supports multiple frameworks
Test cases for free!!!

PexExplorer

Pex understands your code
Pex does not guess
No random inputs
No brute force
Pexanalyzes
Partitions inputs into equivalence classes
One equivalence class per branching behavior
Test inputs computed by Z3 (the constraint solver for program analysis from Microsoft Research)
Performs inter-procedural, path-sensitive analysis
Results:
Small test suite with high test coverage (new test == new branch in code)

Thank You!
And please fill the feedback forms 

Links
http://research.microsoft.com/en-us/projects/contracts/
http://research.microsoft.com/en-us/projects/pex/
http://pexforfun.com/
http://visualstudiogallery.msdn.microsoft.com/en-us/85f0aa38-a8a8-4811-8b86-e7f0b8d8c71b

Software quality with Code Contracts and PEX - CodeCamp16oct2010

by CodeCamp/Iasi on Oct 28, 2010

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Software quality with Code Contracts and PEX - CodeCamp16oct2010 — Presentation Transcript