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Howdy folks,

We’ll have to make this a quick post, since I am only on for a 15 mins break at the SPOC 2010 conference ;-). I prepared a few things, and now I am putting them together.

First of all, I hope you enjoy as much as I do the concept of having VHDs under Windows 7. For those who don’t know where to get started, go to Computer –> Manage –> Disk Management (shown in Figure 1)

image

Figure 1: Disk management. Right-click in order to create or attach VHDs.

And this is where the problem resides. Everytime you want to mount your disks, you have to enter here and execute “Attach Vhd” manually. Not cool enough for us.

The solution: A script, executed as scheduled task (run as Administrator)

These are the steps:

  1. Create a script that calls the diskpart commands
  2. Call the script from a batch file
  3. Create a scheduled task for it.

Sounds simple? It is!

1. Create a script that calls diskpart commands.

image

Figure 2: The attachScript.txt script file.

2. Call the script from a batch file

image

Figure 3: The corresponding batch file: Just calling diskpart with the /s switch and the script file from Figure 2

3. Create a scheduled task for it

image

Step 1: Start –> Accessories –> System Tools –> Task Scheduler

image

Step 2: Set the following fields (Tab: General):

  • Name: Choose what you like. Here: “Mount Vhds”
  • Security options (1): Change User or Group –> Choose an Administrator!
  • Security options (2): Run whether user is logged on or not – makes sense. We don’t need the admin to be logged on for us to access our Vhd, right?
  • Security options (3): Do not store password. You can optionally set this.

image

Step 3: Set “Begin the task” to At startup. Now our task will run at startup.

image

Step 4: Specify which file to run (our created batch/AttachVhds.bat). Confirm by clicking on OK.

That’s it! We’re done! From now on, each time we start the computer, our created task will run!

Important: This is not the most elegant way of automating such a thing, but at the moment there is not a lof of choice under Windows 7. For Windows Server 2008 R2, you can also perform this functionality using PowerShell (and not diskpart/batch files etc.).

I hope you enjoyed this quick tutorial!

Cheers & best greetings from Milan,

Martin

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Howdy folks,

Here we are back again with an introduction of the new features of the upcoming Visual Studio 2010. Its release has been postponed to the 12th of April, so in the meantime we’ll have to stick to the Beta 2, which is pretty stable already. There are so many improvements that we’ll have to divide it into multiple parts. Let’s dive right in!

1. UI: WPF-Based

The UI is now WPF based, which means a better usability and more extensibility options for us developers. Clearly, introducing VS2010 as a WPF-based application is a big push in the direction of visualization and diagramming. We’ll see later how this can be performed using the new IDE.

The editor, for example, is now WPF-based. Cool, but what does that mean for us? Here are the advantages:

Change font size w/ mouse only, or better: No more Options->Change font size during presentations!

Extension Manager allows easy-to-install-and-use add-ins: Also from online galleries – Single click install and enabling!

Highlighting of related variable/method names (Figure 1)

clip_image002

Figure 1: Highlighting related variable. Note that the highlighter correctly references only the name variable passed as a parameter

You can navigate between the highlighted elements using CTRL + SHIFT and the ARROW keys!

2. Intellisense – Improvements:

Method Matching: When VS2010 brings up the list of available methods (after you typed something), it performs not a simple .StartsWith name comparison, but a .Contains. This leads to the results shown on the next screenshots:

Filtered list is gone: When typing letters, the auto completion list that pops up won’t give you all objects/methods/variables that start with the same letter, but only those who are truly related. Consider Figure 3: We typed IF. In the old version, VS would have brought up not only the items shown in the completion list, but possibly many many more, all starting with I (but not containing or continuing with F). Now the IntelliSense search is narrowed, which makes it a lot easier for the developer to select the correct entry.

clip_image004

Figure 2: Highlighting the related object/variable/method.

Case sensitivity: Another nice feature highlighted in figure 2 is the Pascal-Case typing of the capital letters IF, which brings correctly up our method, since its signature contains both I and F as of the method name. Try typing If (f is lowercase), and you won’t find the IsFasterThan method in the auto completion list anymore.

3. References dialog improvements

Remember the Add References dialog in figure 3?

clip_image006

Figure 3: Add references underwent some perception changes.

First of all, Microsoft realized that most people are using it to reference other projects, so they brought up the Projects tab by default. But that’s not all: We all LOVED to wait 30 seconds for the list of .NET or COM objects to appear, right? Because of that, while we are browsing by default the projects, VS2010 is asynchronously loading the available assemblies already. Saves time and nerves.

4. Search and Navigation

Let’s press CTRL + , anywhere in the editor. The window Navigate To will appear, providing us a very powerful search across the entire solution. The search results are updated as we type. From here, we can navigate directly to the found item. Figure 4 shows the dialog.

clip_image008

Figure 4: The Navigate To dialog is a powerful search and navigation mechanism, providing also essential information about the found items. Big improvement over the VS2008 style’s CTRL+SHIFT+F (and subsequent find results crawling without navigation to the desired item)!

5. Call Hierarchy

Remember the Find All References option in the editor’s context menu? It provided us information about where a method/variable has been used. Tell you what. We have a much more powerful way of doing this now: The Call Hierarchy option (Figure 5).

clip_image010

Figure 5: Context menu for the IsFasterThan method, highlighting the new View Call Hierarchy option.

This is the result: A list of all callers (“Calls To”) and callees (“Calls From”) of IsFasterThan (Figure 6). Every caller/callee can be expanded into its own callers/callees. As of figure 6, e.g. Main. This is a really expressive feature which outperforms Find All References by far. However, a possible drawback might be that you could expand the list to infinity by alternating the caller/callee relationship. Figure 6 shows the resulting

image

Figure 6: The View Call Hierarchy window, showing callers/callees of IsFasterThan.

6. Project dialog with search and .NET version selection

Figure 7 shows the improved New Project dialog.

clip_image012

Figure 7: The NewProject dialog. Please note the search field in the right upper corner and the .NET framework dropdown list (center), where now also version 4 of the .NET framework is available.

7. Code Snippets

The code snippets are accessible via the Tools menu, or by pressing the shortcut CTRL + K, CTRL + B

Additional snippets are now available also for HTML, JavaScript and SQL. In sub-categories you can find the different snippets already provided by VS2010. Moreover, you can add your own snippets (as we already know from previous VS versions), as well as remove and import snippets. Figure 8 shows the Code Snippets dialog.

clip_image002[1]

Figure 8: The Code Snippets dialog, showing the newly available languages, as well as subcategories in the Code Snippets Manager.

8. Environment settings: Code Optimized

One more newly available feature is a new default environment setting (remember you had to choose which default settings you wanted to use when starting VS2010 for the first time?). There is one newly available feature which will simply allow you to reduce your viewport to only the code when developing (hence removing the designer). If you have already chosen your first-time-startup environment settings: Don’t worry! The next screenshot explain how you can access the new Web Development (Code Optimized) default environment setting. First, choose Tools –> Import and Export Settings.

image

Figure 9: Import and Export Settings wizard. Choose Reset all settings here. Then you will be prompted whether or not you want to save your current settings. Choose as you wish there. Then proceed.

image

Figure 10: Default environment settings. Note the Web Development (Code Optimized) option, which is new to VS2010. Choose it and VS will immediately switch to those settings, removing e.g. the designer buttons and providing you with a much more lightweight code editor window. Very handy for developers who want to only focus on the code.

9. Conclusion

So I’d say this is about it for this time. Of course there are a lot more features which need to be covered.

The next lessons will deal with creating customized startup pages for VS2010, and introduce the new language features and tools of Visual Studio 2010.

In the meantime, enjoy exploring VS’ new capabilities and features, and hang on till the next time!

Best regards,

Martin

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Dear community,

It’s me once more with a small but handy hint that can make your coding and maintaining a bit easier.

When mapping columns to integral types, it certainly is possible that a field’s value is NULL, right? Now, let’s assume a hypothetical table ORDER that contains a field QUANTITY. Assume also that we have an existing mapping that looks like the one in snippet 1:

   1: <property name="Quantity" column="QUANTITY" type="System.Int32"/>

Snippet 1: Excerpt of a Order table HBM file

Assume also the class we’re mapping to, Order:

   1: public class Order

   2: {

   3:     Int32 Quantity;

   4: ...

Snippet 2: Excerpt of the Order class

Now, what happens to this property once we’re actually mapping values from the DB to it?

If the value is NULL, then the property will assume its default value, which in this case i 0.

So what’s wrong with that?

Simply put, this is correct, but not very effective. Imagine a scenario where we have both 0 and NULL values stored in the QUANTITY column. Once the values are mapped, they could not be distinguished from each other anymore, since they would both map to 0 in our property Order.Quantity.

Hence, we need to come up with a more elegant solution:

We simply use Nullable Types

All you have to do is to change the property Quantity into a Nullable Type, as shown in Snippet 3:

   1: public class Order

   2: {

   3:     Int32? Quantity;

   4: ...

Snippet 3: Excerpt of the changed Order class. Note that the Int32 has been turned into a Int32? Nullable Type.

What else do we have to change? Nothing. NHibernate automatically determines that the property is a nullable type and assigns Null to the property in case of a NULL value arriving from DB.

For the above mentioned scenario, now a 0 would be mapped to a 0 (in the class), and an NULL value from DB would be mapped to an actual Null value (in the class).

That’s it! Enjoy mapping with NHibernate!

Till next time & best regards,

Martin

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Howdy all,

Here comes another post about Code Contracts. Remember my post First Steps with Code Contracts?

Let’s just recall which class we have been working on last time:

   1: namespace Vehicles

   2: {

   3:     class Car : IVehicle

   4:     {

   5:         string name;

   6:         int speed;

   7:

   8:         public Car(string name, int speed)

   9:         {

  10:             this.name = name.ToUpper();

  11:             this.speed = speed;

  12:         }

  13:

  14:         void IVehicle.Drive(int speed)

  15:         {

  16:             Console.WriteLine("Car " + name +

  17:             " is driving at a speed of " + speed);

  18:         }

  19:

  20:         public bool IsFasterThan(Car c2)

  21:         {

  22:             Console.WriteLine(name.ToUpper() +

  23:             " is faster than "

  24:             + c2.name.ToUpper());

  25:             if (this.speed > c2.speed)

  26:                 return true;

  27:             else return false;

  28:         }

  29:

  30:         [ContractInvariantMethod]

  31:         void ObjectInvariant()

  32:         {

  33:           Contract.Invariant(name != null);

  34:         }

  35:     }

  36: }

Snippet 1: The Car class from the First Steps with Code Contracts example.

After completing all the steps from that example, in the end we should have ended up with at least one warning generated by Code Contracts:

Code Contracts: Possibly calling a method on a null reference ‘c2.name’

with respect to line 24.

Now, if we review the usage of Object Invariants (First Steps with Code Contracts), we would see immediately that the purpose of Objects invariants is to provide us a mechanism to perform the checking in ObjectInvariant() in all instances (and instances of subclasses) of Car.

It seems there are no assumptions generated for the Objects Invariants of objects of the same type passed as a parameter (at least not yet, maybe it’ll come).

The workaround:

In order to avoid the warning, we can do 2 things:

  • Assumption:Contract.Assume(!String.IsNullOrEmpty(name)) or
  • Postcondition: Create a property w/ getter postcondition ensuring the result is not null

That should about do the trick!

Enjoy and see you next time!

Martin

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Howdy,

The Code Contracts User Manual holds (besides detailed information about Code Contracts’ usage, advantages and drawbacks) a few nice lists of Code Snippets that ship with the Code Contracts and will ease your life. Find below the list of available Code Snippets for the C# language, as exactly taken from the User Manual (January 12th, 2010):

cr Contract.Requires(…);
ce Contract.Ensures(…);
ci Contract.Invariant(…);
crr Contract.Result<…>()
co Contract.OldValue(…)
cim [ContractInvariantMethod]

private ObjectInvariant()

{

Contract.Invariant(…);

}

crn Contract.Requires(… != null);
cen Contract.Ensures(Contracts.Result<…>() != null);
crsn Contract.Requires( !String.IsNullOrEmpty(…) );
cesn Contract.Ensures( !String.IsNullOrEmpty(Contracts.Result<string>()) );
cca Contract.Assert(…);
cam Contract.Assume(…);
cre Contract.Requires<E>(…);
cren Contract.Requires<ArgumentNullException>(… != null);
cresn Contract.Requires<ArgumentException>( !String.IsNullOrEmpty(…) );
cintf expands to an interface template and associated contract class

If you plan to use Code Contracts effectively, this list comes in very handy. I hope it’s of use for you. In the Code Contracts User Manual, you can find a similar list also for Visual Basic.

Best regards,

Martin

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Howdy ladies and gents out there,

Here we go with another NHibernate common problem solved for you. Recently the question arose whether it is possible or not to execute a query with NHibernate that checks whether a property lies in a given range of values or not. Not much of a problem, we would say, since HQL can do it just directly using its SQL-like syntax. For example, if we recall our example DevJour1 from part 1 of the NHibernate noob series, we could define a query in the Book.hbm.xml file:

   1: <query name="GetAllBooksWithinRange">

   2:   <![CDATA[

   3:     select b from Book b where b.Title in ('It', 'Salem's Lot',                                                  'Langoliers');

   4:   ]]>

   5: </query>

Snippet 1: Excerpt from the Book.hbm.xml file: HQL query returning all books whose title lies within a certain range of values.

Problem solved? Not quite. Another requirement to this query was to provide custom sorting w/ a custom field and a custom sort direction. Sounds familiar, doesn’t it? Remember our first NHibernate troubles post: Custom Sorting. Simply put, using HQL, this is not possible. So we had to use Criteria queries. But how do we implement the range value check for a given property using Criteria queries? It’s simple, really:

   1: public static List<Book> GetAllBooksWithinRange()

   2: {

   3:     String[] titles = { "It", "Salem's Lot", "Langoliers" };

   4:     ISession session = Program.OpenSession();

   5:     List<Book> books = session.CreateCriteria(typeof(Book)).

   6:         Add(Restrictions.In("Title", titles)).

   7:         List<Book>().ToList<Book>();

   8:     return books;

   9: }

Snippet 2: Excerpt from the Book class.

BookGetAllBooksWithinRange()explained (line by line):

3: Definition of our range of values

4: Opening a session, recall from Program class of the Custom Sorting article.

5: Creating criteria for type Book .

6: Crucial part: Adding Restrictions.In (NHibernate.Criterion), passing the property that needs to be checked (Title) and the list of range values.

7-8: Calling the List() method(s) and returning the retrieved list

Important: This works also, when comparing a property of a property with a range of values. Example: Assuming, Book contains a class Author , which in turn contains a property Surname. Then we could formulate such a comparison statement like follows:

.Add(Restrictions.In(“Author.Surname”, names)).


Under the assumption that names is an array containing strings.

That’s it! I’m sure there are more problems to be solved!

See you later!

Best regards,

Martin

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Hello all,

This time we’ll do a quick exploration of how we can apply Code Contracts to interfaces. As you know from our post First Steps with Code Contracts, the preconditions and postconditions (Contract.Requires and Contract.Ensures calls, respectively) must be placed inside a method body.

Therefore, when defining an interface, we run into a problem: We do not have method bodies there. Of course we could put such calls inside each effective implementation of the interface methods. Clearly, this is not what we want, since

  • We do not want to replicate code in x classes that implement our interface and
  • Future implementations of our interface would contain the conditions we need

Luckily, the Code Contracts provide us with a powerful mechanism that allows us to define a class which implements that interface and which will do the necessary checks.

The Contract Class

Let’s see how this is done, right? For this example, please recall our example from the First Steps with Code Contracts introductory article.

 

   1: namespace Vehicles

   2: {

   3:     interface IVehicle

   4:     {

   5:         void Drive(Int32 speed);        

   6:     }

   7: }

Snippet 1: The IVehicle interface

Also do recall that we did not define any pre- or postconditions for our interface (how could we? – there is no method body).

This is exactly the place, where we will put a so called Contract Class, that will implement our interface. Every time the interface is called, the conditions put into our Contract Class will be injected. This holds for every implementation of our interface.

We basically need two things:

1. A class that implements our interface IVehicle that is marked as Contract Class via an attribute:

 

   1: [ContractClassFor(typeof(IVehicle))]

   2: public class IVehicleContract : IVehicle

   3: {

   4: }

Snippet 2: Contract Class implementing the interface we want to fulfil requirements

2. Another class that links up our interface to the ContractClass

   1: [ContractClass(typeof(IVehicleContract))]

   2: public partial interface IVehicle

   3: {

   4: }

Snippet 3: The link between the interface and our Contract Class

Hint: Don’t worry: You do not have to implement these two classes from scratch: The Code Contracts come with a bunch of predefined snippets that can be executed right away. The following snippet will do the trick for generating the Contract Classes for an interface:

 

cintf ->(TAB – TAB)

The next step is to implement the interface for IVehicleContract.

clip_image002

Figure 1: Explicitly implementing the interface IVehicle for the IVehicleContract class.

The result is shown in Snippet 4:

   1: [ContractClassFor(typeof(IVehicle))]

   2: public class IVehicleContract : IVehicle

   3: {

   4:     void IVehicle.Drive(int speed)

   5:     {

   6:         throw new NotImplementedException();

   7:     }

   8: }

As a next step, we can implement our conditions in the method body of IVehicle.Drive method in IVehicleContract, like shown in Snippet 5:

   1: [ContractClassFor(typeof(IVehicle))]

   2: public class IVehicleContract : IVehicle

   3: {

   4:     void IVehicle.Drive(int speed)

   5:     {

   6:         Contract.Requires(speed >= 0);

   7:     }

   8: }

Snippet 5: precondition in interface method implementation.

What does this mean now? Well, for every implementation of the interface IVehicle , the code precondition will be injected. In other words:

 

The condition we define in the Contract Class must hold for all implementations of the interface.

 

That was it already (for this time)! It is as simple to use as it seems.

 

Enjoy and stay tuned for the next time!

Best regards,

Martin

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Hello all,

Today we are going to talk about another exciting project from the Microsoft Research Labs: Code Contracts. It is a Design-By-Contract (DbC) system, that enables us as developers to formulate the expected behaviour of our code by directly putting it into the code.

The main tools of applying Code Contracts are:

  • Static checking (checks contracts at compile time)
  • Runtime checking (checks contracts at runtime)
  • Automated documentation generation (keeps code and docs in sync)

Prerequisites

Before we get started using Code Contracts. I used the following environment for carrying out the tests with Code Contracts:

  • Windows 7
  • Visual Studio 2010 Beta 2 Ultimate*
  • Code Contracts Tools*

Important: I used Visual Studio 2010 Beta 2, because it contains the .NET framework 4, which already includes the Code Contracts framework. You could also use them with VS2008, if you installed the .NET framework 4. The Code Contract Tools need to be downloaded separately. I highly recommend them, since they will add a new pane to your VS2010 which in turn lets you set various options, like enabling the static checker directly from the UI.

1.1 The Strengths of Code Contracts

Elevating assertions to the API level. At this point, the specification of code is not only somewhere deeply hidden in the method, but immediately visible to the caller (if, for example, a Contract is not fulfilled). On the other side, a caller now can know perfectly what to expect from a method.

1.2 Code Contracts for Methods

First, we are going to show how to implement Code Contracts on the method level.

We’ll start with the creation of a test project that will serve our purposes of showing Code Contracts’ capabilities:

image

Figure 1: Add a new console application and name it Vehicles

As a next step, we create a class and an interface, namely Car and IVehicle. Implement them as follows in the snippets 1 and 2. Leave the automatically generated Program class – we’ll need it later for running our examples.

   1: using System;

   2: using System.Collections.Generic;

   3: using System.Linq;

   4: using System.Text;

   5:

   6: namespace Vehicles

   7: {

   8:     interface IVehicle

   9:     {

  10:         void Drive(Int32 speed);

  11:     }

  12: }

Snippet 1: Interface IVehicle, defining one method signature

   1: namespace Vehicles

   2: {

   3:     class Car : IVehicle

   4:     {

   5:         string name;

   6:         int speed;

   7:

   8:         public Car(string name, int speed)

   9:         {

  10:             this.name = name.ToUpper();

  11:             this.speed = speed;

  12:         }

  13:

  14:         void IVehicle.Drive(int speed)

  15:         {

  16:             Console.WriteLine("Car " + name +

  17:             " is driving at a speed of " + speed);

  18:         }

  19:

  20:         public bool IsFasterThan(Car c2)

  21:         {

  22:             Console.WriteLine(name.ToUpper() +

  23:             " is faster than "

  24:             + c2.name.ToUpper());

  25:

  26:             if (this.speed > c2.speed)

  27:                 return true;

  28:             else return false;

  29:         }

  30:     }

  31: }

Snippet 2: Class Car implementing IVehicle.

So far, so good, right? Nothing special there, and the code has got very simple “functionality”. A car that can drive, alright. And check whether it is faster than another car. Compiling the project reveals a succeeding build which at first sight contains no errors.

Before we take further steps, let’s activate the Static Checking feature of Code Contracts. In order to enable this, just right-click the project Vehicles -> Properties.

The last pane on the bottom of the Properties’ window is called Code Contracts. Go for it.

clip_image004

Figure 2: The Code Contracts’ configuration in Properties. Then proceed with Figure 3.

image

Figure 3: Enable static contract checking and the checking of implicit non-null obligations.

Compile again, and in the warning sections, we’ll receive a bunch of warnings generated by Code Contracts:

image

Figure 4: Warning list, generated by Code Contracts.

Those messages are suggestions of how we should change our code in order to be (more likely to be) safe from exceptions.

The warnings, line by line:

1-2: Tell us that we should add a pre-condition in order to be sure from NullReferenceExceptions when accessing the property name (1) or passing a parameter that could be possible equal to null (2). The cool thing is: Code Contracts even provide us with the correct code in order to achieve this.

3-5: These are the actual warnings, containing possible failures.

Preconditions

A precondition is simply added by using the following method:

Contract.Requires(condition)

When debugging, we can step over such a call and verify that it is actually executed. The call is made in the method body, at any desired position. Usually it is placed at the beginning.

Postconditions

A postcondition is simply added by using the following method:

Contract.Ensures(condition)

When debugging, we cannot step over such a call (to be precise: not at the position where we put it in the code), since it is not actually executed in the method body, but only afterwards. Once we stepped over the complete method, we arrive at the Contract.Ensures call. The following snippet show how pre- and postconditions can be applied to the methods of our class Car:

   1: using System;

   2: using System.Collections.Generic;

   3: using System.Linq;

   4: using System.Text;

   5: using System.Diagnostics.Contracts;

   6:

   7: namespace Vehicles

   8: {

   9:     class Car : IVehicle

  10:     {

  11:         string name;

  12:         int speed;

  13:

  14:         public Car(string name, int speed)

  15:         {

  16:             Contract.Requires(name != null);

  17:             this.name = name.ToUpper();

  18:             this.speed = speed;

  19:         }

  20:

  21:         void IVehicle.Drive(int speed)

  22:         {

  23:             Console.WriteLine("Car " + name +

  24:             "is driving at a speed of " + speed);

  25:         }

  26:

  27:         public bool IsFasterThan(Car c2)

  28:         {

  29:             Contract.Requires(c2 != null);

  30:             Console.WriteLine(name.ToUpper() +

  31:             " is faster than " +

  32:             c2.name.ToUpper());

  33:

  34:             if (this.speed > c2.speed)

  35:                 return true;

  36:             else return false;

  37:         }

  38:     }

  39: }

Snippet 3: The Car class, using Code Contracts’ preconditions

After we added the Contract.Requires calls in IsFasterThan and in the Car ctor, we receive only 2 warnings from Code Contracts. Just compile to verify that.

Why still two warnings? We added preconditions to check that!

The reason: Only our method IsFasterThan in this particular class, Car, requires name to be non-null. But we could have for example a subclass inheriting from Car, which does not perform the same check. Hence, we need to take care for that. And in fact, Code Contracts provides us the necessary means in order to ensure that no object deriving from Car, can have name which is null:

   1: [ContractInvariantMethod]

   2: void ObjectInvariant()

   3: {

   4:     Contract.Invariant(name != null);

   5: }

Snippet 4: Object invariants

Calling again reveals that the warning concerning the name variable of class Car has gone. Good! It means, we are safe from accessing a null value – variable, and all other programmers subclassing our Car are safe, too!

This is it for now! Next time we’ll see how to deal with Code Contracts and interfaces.

Enjoy playing with Code Contracts and see you soon!

Best regards,

Martin

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Howdy folks,

So far, we have seen how to let Pex automatically generate unit tests, and how to generate PUT customizations while testing interfaces.

However, there are a few cases you might come across, where Pex cannot generate test cases for your code. This is the case, if you try to test code that is:

  • Environment dependent
  • Dependent on sealed classes, static methods, non-public constructors, etc.

Since these might represent non-deterministic outcomes, Pex is not able to generate test cases.

To cite the “Testability” slide of the Tutorial “Parametrized Unit Testing: Principles, Techniques, and Applications in Practice” (Tillmann, de Halleux, Schulte, Xie):

Pex understands managed .NET code only.

Pex does not understand native code.

Examples for such method calls might be:

  • Machine-dependent dates, such as calls to DateTime.Now
  • Methods that read or write from the network, hard drive, databases, etc…

Alright, so there is untestable code, but we want to test it anyway. The good news is: We can do it. Pex works tightly together with a framework called Moles (since January 15th, formerly known as Stubs framework)

1.1 A Practical Example of the Problem

We’ll show by example where the problem is: We change our Store class from the post {TODO. PEX 1}, because we also want to output the date on which the delivery started. The resultung method can be seen in Figure 1:

   1: public void DeliverToAddress(String address, Book book)

   2: {

   3:     String deliveryMsg = "Book w/ title" + book.Title +

   4:                          "delivered to " + address +

   5:                          "on " + DateTime.Now;

   6:     Console.WriteLine(deliveryMsg);

   7: }

Snippet 1: Change of the DeliverToAddress method.

Let’s look at line 5: We access DateTime.Now. Everything’s fine, you say? But not for Pex, since DateTime.Now is machine-dependent. Let’s have a look at what Pex generates, so. Right-click on DeliverToAddress and select what? Exactly:

Run Pex.

A look at the Pex UI immediately tells us, that there is something wrong with the generation of the test cases. A button appears stating that there are 4 uninstrumented methods. Figure 1 shows  the Pex UI and the newly appearing button:

image

Figure 1: Uninstrumented code/testability issues when using native code.

A click on the button reveals there have been calls to machine-time-dependent methods, which cannot be tested by Pex. Obviously, these method were (implicitly) invoked by the call to DateTime.Now. The result is shown below:

image

Figure 2: List of the testability issues, after hitting the 4 Uninstrumented Methods – Button

1.2 A Possible Solution: Detouring

Now, in order to make such code testable, the principle would be, to replace such methods with a delegate. In our case, the call to File.Open() could be replaced like that:

DateTime.Now = () => new DateTime(2010, 1, 20);

Unfortunately, this is simply not possible. Therefore, the Pex team came up with a workaround: Moles. Since we cannot replace the original classes and their methods, we construct our own classes and methods that will do the necessary detouring. There is a simple rule about the naming convention:

Prefix M + Original class name + . + Original method name + Suffix;

Now, with our own class, we can do the passing to a delegate which returns a deterministic result. In our case, DateTime.Now would become:

MDateTime.NowGet = () => new DateTime(2010, 1, 20);

Short and sweet: For every class (or struct), we can produce a Mole Class, which performs a detouring of the original call to the value we assign using a lambda expression (or anonymous method).

1.3 Generation of the Mole Classes

Do we have to generate the classes on our own? Nope. We basically create an XML file with the .stubx file extension, which states for which classes there should be generated a Mole (or a Stub). And the good news is:

The framework will generate the actual stubs and moles!

Here is how we are going to do it:

  • Right-click BookStoreTest –> Add New Item –> Stubs and Moles for Testing
  • Leave the proposed name as it is (for now) –> Add

image

Figure 3: Selecting the Stubs & Moles for Testing template

The generated Assemblies1.stubx will look like follows:

   1: <Stubs xmlns="http://schemas.microsoft.com/stubs/2008/">

   2:   <Assembly Name="Assemblies1" />

   3: </Stubs>

Snippet 2: The generated .stubx file, referring to a nonsense Assembly, Assemblies1.

As a next step, we need to tell via the .stubx file (which is nothing more than an XML file), for which classes, in which Assembly etc. we want to generate Moles. The following code snippet shows you how to do this:

   1: <Stubs xmlns="http://schemas.microsoft.com/stubs/2008/">

   2:   <Assembly Name="mscorlib" />

   3:   <StubGeneration Disable="true"></StubGeneration>

   4:   <MoleGeneration Disable="false">

   5:     <TypeFilter Namespace="System" TypeName="DateTime"/>

   6:   </MoleGeneration>

   7: </Stubs>

Snippet 3: The .stubx file defining the classes for which we want Moles to be generated.

Assemblies1.stubx, Explained (line by line)

1: The Stubs tag only defines that we are dealing with Stub/Mole generation

2: The Name attribute specifies the Assembly, in which our “problem class” resides in: DateTime belongs to mscorlib, so with add this one.

3: We turn Stub generation off, since it is not needed at this point

4: MoleGeneration: We specify our desired class by adding a <TypeFilter> tag, containing the namespace of our class and the class name.

Again, simple, right? Basically, we specified only three things:

  • Assembly
  • Namespace
  • Class name

That’s it. Once we save our file, magic happens and the Moles framework generates the Mole classes in the background. The output window shows us the current progress of the Mole class generation:

image

Once the generation is done, we can proceed to the final step: Using the Mole class to detour the actual call to DateTime.Now to our newly generated MDateTime.NowGet, or in other words: Let’s see the Mole class in action!

Therefore, we need a little modification to the StoreTest.DeliverOrders (which will then implicitly call DeliverToAddress, multiple times):

   1: [PexMethod]

   2: public void DeliverOrders([PexAssumeUnderTest]Store target)

   3: {

   4:     int count = 0;

   5:     var storage = new SIStorage()

   6:     {

   7:         DeliverToAddressStringBook = 
              (String address, Book book) => count++;

   8:     };

   9:

  10:     MDateTime.NowGet = () => new DateTime(2010, 1, 20);

  11:

  12:     target.DeliverOrders();

  13: }

Snippet 4: Excerpt of our changed DeliverOrders testing method.

The important line is line 10:

We added the Mole Class, which will now detour all calls to DateTime.Now to MDateTime.NowGet and eventually produce a new DateTime.

If we wanted to tell Pex that we want to test the code not for a specific DateTime, as shown in Snippet 4, line 10, we simply could elevate our DateTime to a parameter and pass it in the lambda expression instead of new DateTime(2010, 1, 20);

So, we are actually done for this time.

One more thing: In order to successfully be able to reference the newly generated MDateTime class, you must make use of the following namespace:

   1: using System.Stubs;

Snippet 5: Make use of the correct namespace in order to make the Mole classes visible.

Epilogue

That’s it!

I hope this short article could give you an idea of:

  • Which code can “normally” be tested using Pex
  • What you have to do when Pex encounters untestable code
  • That untestable means no more untestable

Enjoy the testing and have fun exploring the capabilities of Pex and the Mole framework!

Stay tuned for the next time, when we’ll talk about Code Contracts!

Best regards,

Martin

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Hello,

You might already guess it: Pex won’t let me go, and so I’d like to explain in short a few of Pex’ concepts.

1.1 Code Coverage

Pex is an abbreviation for Program Exploration. You guessed it: Nomen est omen. It analyzes the branches (if, then, else, etc…) of control flow and tries to cover each and every branch. This leads to a highly elevated code coverage, or, in other words: It helps to increase the amount of tested code.

1.2 The Main Idea of Parametrized Unit Testing using Pex

…is to elevate any values that should not matter (i.e. that should not influence the program’s runtime behaviour) into parameters. Pex will then care about how to deal with them, about creating test cases for all possible values they can assume. Short & sweet: Pex cares about your parameters and helps to ensure there are no cases where your program would fail because of them.

1.3 The Nuts and Bolts of a PUT

Figure 1 gives you an example of what a Parametrized Unit Test (PUT) looks like:

image

Figure 1: A simple PUT

We just use the [PexMethod] attribute to denote that the following method is a PUT.

Sometimes we need some of the parameters to be null, in order to get a method running at all. In such a case, we can give Pex the instruction not to generate tests which would assume that parameter as NULL. We simply do this by adding the attribute

[PexAssumeUnderTest]

in front of the parameter type. Sounds straightforward, doesn’t it?

Within the PUT method, you can (as suggested by Pex upon generationg of the tests) multiple assertions to ensure the correct behaviour of the method. What Pex does for you, is the following:

  • Detecting dereferencing of potential null values (and generates a test case)
  • Analysis of e.g. loop boundaries (and generates test cases for each assumable value, including boundary values)

There is only one drawback: This way of testing only works as long as we have implemented method bodies. Are there cases where we don’t have them? Of course: Interfaces. Let’s see how Pex deals with interfaces.

1.4 Extending our Example

In order to see how Pex generates test code for interfaces, we need to add an interface to our project BookStore (which we created in Pex – Automated White Box Unit Testing).

   1: using System;

   2: using System.Collections.Generic;

   3: using System.Linq;

   4: using System.Text;

   5:

   6: namespace BookStore

   7: {

   8:     public interface IStorage

   9:     {

  10:         void DeliverToAddress(String address, Book book);

  11:     }

  12: }

Snippet 1: The IStorage interface.

As a next step, we are going to use it somewhere, namely: We let our class Store implement IStorage.

public class Store : IStorage

Please note that the IStorage member method DeliverToAddress(…) has already been implemented in our previous post. Hence, the code should compile as soon as you implemented the changes.

What comes next? Pex cannot possibly know about our newly created interface, so we need to tell it somehow to generate stubs for the interface. And how do we do that?

Re-run Pex!

For that, right-click on the project BookStore and select Run Pex from the context menu. Pex generated the following class:

   1: public partial class SIStorage : IStorage

   2: {

   3:     Action<string, global::BookStore.Book> DeliverToAddressStringBook;

   4:     void DeliverToAddress(string address, Book book)

   5:     {

   6:         return DeliverToAddressStringBook(address, book);

   7:     }

   8: }

Snippet 2: The generated stub class for the IStorage interface: SIStorage.

As shown in Snippet 2, the generator creates a class named S + <interface name>, which implements the interface. For each method defined in the interface, a property (a delegate, in fact)will be added which resembles the method’s signature (method name + parameters’ types, camel case).

1.5 Customizing the stub

Now we’ll dig a little deeper. We modify our DeliverToAddress method from Snippet 1. Why do we do this? We simply double-check that the amount of ordered books is equal to the amount of the actually delivered book.

   1: // <copyright file="StoreTest.cs" company="Scientific Network">Copyright © Scientific Network 2010</copyright>

   2:

   3: using System;

   4: using BookStore;

   5: using Microsoft.Pex.Framework;

   6: using Microsoft.Pex.Framework.Validation;

   7: using Microsoft.VisualStudio.TestTools.UnitTesting;

   8: using BookStore.Stubs;

   9: using System.Collections.Generic;

  10:

  11: namespace BookStore

  12: {

  13:     [TestClass]

  14:     [PexClass(typeof(Store))]

  15:     [PexAllowedExceptionFromTypeUnderTest(typeof(ArgumentException),

  16:                                     AcceptExceptionSubtypes = true)]

  17:     [PexAllowedExceptionFromTypeUnderTest(

  18:             typeof(InvalidOperationException)

  19:     )]

  20:     public partial class StoreTest

  21:     {

  22:         [PexMethod]

  23:         public void DeliverOrders([PexAssumeUnderTest]Store target)

  24:         {

  25:             int count = 0;

  26:             var storage = new SIStorage()

  27:             {

  28:                 DeliverToAddressStringBook =

  29:                 delegate(String address, Book book)

  30:                 {

  31:                     count++;

  32:                 }

  33:             };

  34:             target.DeliverOrders();

  35:             Assert.AreEqual(CalculateExpectedDeliveries(target.Orders), count);

  36:             // TODO: add assertions to method StoreTest.DeliverOrders(Store)

  37:         }

  38:

  39:         private int CalculateExpectedDeliveries(List<Order> orders)

  40:         {

  41:             int deliveries = 0;

  42:             foreach (Order order in orders)

  43:             {

  44:                 deliveries += order.Quantity;

  45:             }

  46:             return deliveries;

  47:         }

  48:     }

  49: }

Snippet 3: The modified stub.

StoreTest explanantion, (line by line)

Don’t worry! It looks more complicated than it actually is. The real stuff starts only on line 25.

25: Declaring a counter variable which will serve our comparison

26-33: Declaring an anonymous method that will simply increase a counter each time DeliverToAddressStringBook is called.

34: Perform the actuall delivery, calling DeliverOrders, which itself will call DeliverToAddress.

35: Using an assertion in order to determine whether our expected amount of delilveries (CalculateExpectedDeliveries) equals the actual amount of delivered books (count).

39-47: The method CalculateExpectedDeliveries is only used to retrieve the correct amount of books that is expected to be delivered by the DeliverOrders method.

In order to let the tests run, simply right-click on the DeliverOrders method and choose Run Pex Explorations, as shown in Figure 2.

image

Figure 2: Run Pex on the PUT.

At this point, you will perhaps notice failing tests where the order.Quantity is equal to a negative number.

I’d like to show you a simple means to prevent Pex from generating and running test cases under certain circumstances: Code Contracts.

For this post, I just show you what you need for that purpose. We’ll probably cover Code Contracts in a future post, since they integrate very well with Pex (and vice versa).

Just drop a statement like

Contract.Assume(target.Orders.Count >= 0);

at the beginning of the DeliverOrders method. For Pex, this simply means to ignore all cases where the store would get a negative amount of orders – hence preventing Pex from generating nonsense test cases.

1.6 Why all this Work?

The advantage of all this customization should be clear: You can test an interface in general, without having to test all single methods that implement the interface.

I hope you are familiar now with (customizable) PUTs and interface tests.

Cheers, and see you at the next post!

Martin

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