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Nbuilder - A rapid test object generator.

Through a fluent, extensible interface, NBuilder allows you to rapidly create test data, automatically assigning values to properties and public fields that are one of the built in .NET data types (e.g. ints and strings). NBuilder allows you to override for properties you are interested in using lambda expressions.

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How can NBuilder help?

This test data has a variety of uses. For example:

  • For automated functional and acceptance tests.
  • Returning the data from a stubbed service.
  • Creating test data for use when developing or testing an application.
  • Performance tuning with large amounts of data.

Major features


Easily persist generated objects using Persist()

NBuilder also allows you to easily set up persistence. You do this by telling NBuilder how to persist your objects. The most convenient place to do this would be in an NUnit SetUpFixture class.

var repository = new ProductRepository();

Once you have done this, it's simply a case of calling Persist() instead of Build():


Hierarchy generation

Easily create hierarchies of objects by telling NBuilder how to add children to your object. You can even persist the hierarchies just by giving NBuilder create and update methods.

You can easily create a random hierarchy by first creating an initial list and then calling BuildHierarchy(), and passing in a specification.

var hierarchySpec = Builder<HierarchySpec<Category>>.CreateNew()
                .With(x => x.AddMethod = (parent, child) => parent.AddChild(child))
                .With(x => x.Depth = 5)
                .With(x => x.MaximumChildren = 10)
                .With(x => x.MinimumChildren = 5)
                .With(x => x.NamingMethod = (cat, title) => cat.Title = "Category " + title)
                .With(x => x.NumberOfRoots = 10).Build();


This will create a category tree and by supplying a naming method, will even name your categories with their path in the tree. For example:

 Category - Title = "1"
      Category - Title = "1.1"
      Category - Title = "1.2"
  Category - Title = "2"
      Category - Title = "2.1"
          Category - Title = "2.1.1"
      Category - Title = "2.2"
      Category - Title = "2.3"


NBuilder is highly configurable. Through the BuilderSetup class you can control how NBuilder names objects and disable naming for certain properties of certain types.

Custom persistence service

Easily add your own custom persistence service, allowing you to use any ORM.

BuilderSetup.SetPersistenceService(new MyCustomPersistenceService());
Turning off automatic property naming

If you don't want properties to be automatically given values, you can simply turn it off.

BuilderSetup.AutoNameProperties = false;
Changing the default property namer

You can change the default property namer to use the random value property namer, or you can create your own either from scratch implementing the IPropertyNamer interface, or by extending one of the classes, for example to add support

BuilderSetup.SetDefaultPropertyNamer(new RandomValuePropertyNamer());
Adding a property namer for a specific type

If, for example, you have a class that has a custom struct, NBuilder will ignore this property because it doesn't know how to set it. You could overcome this by adding a special property namer, just for Products.

BuilderSetup.SetPropertyNamerFor<Product>(new CustomProductPropertyNamer(new ReflectionUtil()));
Disabling automatic property naming for a specific property of a specific type

If you don't want values to automatically be assigned to certain properties, you can disable it like this:

BuilderSetup.DisablePropertyNamingFor<Product, int>(x => x.Id);


Through extension methods you can extend NBuilder's fluent interface to add custom building functionality. You can also create custom property namers globally or for specific types.

Custom declarations

In NBuilder nearly all of the public interface is implemented with extension methods. This of course means it's possible to add your own.

For example, out of the box the list builder has seven 'declarations' All(), WhereRandom(n), WhereRandom(n, start, end), WhereTheFirst(n), WhereTheLast(n), AndTheNext(n), AndThePrevious(n). However if you wanted to add your own,

e.g. to return all the even or odd items, all you need to do is write a new extension method - WhereAllEven()

"Operable" extensions

If, for example, you find yourself repeating yourself when creating test data and you want to wrap something up in a method, you can do this by extending IOperable. You can do this generically or per-type.

For example say if rather than saying:

	.Have(x => x.Title = "12345....[LongString].....12345")

You could instead create an extension method:

public static IOperable<Product> HaveLongTitles(this IOperable<Product> operable)
    ((IDeclaration<Product>) operable).ObjectBuilder.With(x => x.Title = "12345....[LongString].....12345");
    return operable;

Giving you the ability to say:


You could of course make it even more succinct by adding an extension method to IListBuilder

public static IListBuilder<Product> WhereAllHaveLongTitles(this IListBuilder<Product> listBuilder)
    var listBuilderImpl = (IListBuilderImpl<Product>) listBuilder;
    var declaration = new GlobalDeclaration<Product>(listBuilderImpl, listBuilderImpl.CreateObjectBuilder());
    declaration.Have(x => x.Title = "12345....[LongString].....12345");

    return declaration;

This would allow you to say:


For more examples, please check the functional tests

Until the full documentation is available please have a look at the functional tests in the source code. These explain how to do everything that's currently possible in NBuilder.

Continuous Integration

NBuilder uses AppVeyor for continuous integration.


Rapid generation of test objects in .NET




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