Skip to main content

PEX - Automated Exploratory Program Testing

One of the prodcuts that is being reserched at Microsoft is PEX (program exploration).The team released a 0.5 version product last month and you can download it here.So what is PEX anyway, what does it try to solve?, Remeber how you wrote a method with "amazing" logic and you also wrote nice test cases to test this function, if the function is not very complex and have only a few paths it can take, you would end up with maybe a test case or two and some set of input data.But if your function is very complex and has a complex , you have to go through each and every path the program would take and generate you test data (and not to metion the test cases).
What PEX does is, it "scans" your program (the method you want to test) and comes with a set of test data for each and every path. Lets take an example.

[TestMethod] // mark this as a test case
[PexMethod] //PEX attribute
public void TestMethod1(int i, int y)
{
GetNumber(i, y);
}

//The method you want to test
private int GetNumber(int i, int y)
{
int j = i / y;
if (j > 0)
return 0;
else
return 1;
}

The example is explantory (I have used MS Test), but with a few exceptions that the test case is now parameterized, to take in the parameters needed by the function that is being tested. And also you can see that a [PexMethod] attribute is added on top of the test case for PEX to recognize the test case.

You can see, that PEX created data for all possible paths of the function. Running PEX on your methods would also ensure that you delt with the most unexpected inputs as well, for an example an exception that might turn out for a value that the user passed into method that you never thought about in your test cases, making your program stable (in this example a DivideByZeroException, and if we had more paths our function could have taken, PEX would generate more test cases).

PEX work with .NET 2.0 and higher, there is also a VS 2008 add-in that you can use. Currently PEX is supports MS TEST, but they are planning to write extensions for other test tools as well.

A cool thing about PEX, is that it creates code for each and every test case it creates, so that also means that you can debug the generated test cases.

Comments

Post a Comment

Popular posts from this blog

Hosting WCF services on IIS or Windows Services?

There came one of those questions from the client whether to use II7 hosting or windows service hosting for WCF services. I tried recollecting a few points and thought of writing it down. WCF applications can be hosted in 2 main ways - In a Windows service - On IIS 7 and above When WCF was first released, IIS 6 did not support hosting WCF applications that support Non-HTTP communication like Net.TCP or Net.MSMQ and developers had to rely on hosting these services on Windows Services. With the release of IIS 7, it was possible to deploy these Non-Http based applications also on IIS 7. Following are the benefits of using IIS 7 to host WCF applications Less development effort Hosting on Windows service, mandates the creating of a Windows service installer project on windows service and writing code to instantiate the service, whereas the service could just be hosted on IIS by creating an application on IIS, no further development is needed, just the service implementa...
4 comments
Read more

Finalization, Know What it Costs

This is a post about object finalization in .NET. Finalization is not as inexpensive as we think, it increases the pressure put on GC.All objects that need finalization are moved into a finalizable queue and the actual finalization happens in a separate thread. Because the objects full state may be needed, the object itself and all the object it points to are promoted to the next generation (this is needed so that GC does not clean these objects off in the current round), and these objects are cleaned up only after the following GC. Due to this reason, resources that need to be released should be wrapped in as small a finalizable object as possible, for instance if your class needs a reference to an unmanaged resource, then you should wrap the unmanaged resource in a separate finalizable class and make that a member of your class and furthermore the parent should be a non-finalizable class. This approach will assure that only the wrapped class (class that contains the unmanaged resourc...
1 comment
Read more

The maximum nametable character count quota (16384) has been exceeded

Some of our services were growing and the other day it hit the quote, I could not update the service references, nor was I able to run the WCFTest client. An error is diplayed saying " The maximum nametable character count quota (16384) has been exceeded " The problem was with the mex endpoint, where the XML that was sent was too much for the client to handle, this can be fixed by do the following. Just paste the lines below within the configuration section of the devenve.exe.config and the svcutil.exe.config files found at the locations C:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE , C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin Restart IIS and you are done. The detailed error that you get is the following : Error: Cannot obtain Metadata from net.tcp://localhost:8731/ Services/SecurityManager/mex If this is a Windows (R) Communication Foundation service to which you have access, please check that you have enabled metadata publishing at the specified address. F...
5 comments
Read more