Walkthrough: Using TDD with ASP.NET MVC

Article
02/21/2011

This walkthrough shows you how to develop an ASP.NET MVC application in Visual Studio using the test-driven development (TDD) approach. MVC was designed to enable testability without requiring dependencies on a Web server (IIS), on a database, or on external classes. (This is in contrast to unit tests for Web Forms pages, which require a Web server.)

In this walkthrough, you will create tests for an MVC controller before you implement the controller functionality. You can write tests before you have a controller. The advantage is that compiler errors in your unit tests are then a first-level form of unit-test failure. The emphasis is on how to design the intent of the controller by writing unit tests before implementing the controller itself, which is an important aspect of the TDD philosophy. (For a good overview of the MVC TDD philosophy, see the entry It’s Not TDD, It’s Design By Example on Brad Wilson's blog.)

In the walkthrough, you will create a project and unit tests for an application that you can use to display and edit contacts. A contact has a first name, last name, phone number, and an email alias.

A Visual Studio project with source code is available to accompany this topic: Download. The download contains the completed ASP.NET MVC C# and Visual Basic projects (in the cs and vb folders) and C# and Visual Basic projects in the QuickStart folder. The first part of this walkthrough shows how to create an MVC project in Visual Studio, how to add a data model, and how to add metadata to the data model. If you know how to create an ASP.NET MVC project and an Entity Framework data model, you can use the projects that are in the downloadable project under the QuickStart folder instead and skip to the section Adding a Repository later in this walkthrough.

Prerequisites

In order to complete this walkthrough, you will need:

Microsoft Visual Studio 2008 Service Pack 1 or later.

Note

Visual Studio Standard Edition and Visual Web Developer Express do not do not support unit-test projects.
The ASP.NET MVC 2 framework. To download the most up-to-date version of the framework, see the ASP.NET MVC download page.
The Contact.mdf database file. This database file is part of the sample project that you can download for this project: Download

Creating a New MVC Application with Unit Tests

In this section, you create a new Visual Studio solution that includes both the application project and a test project.

Note

This walkthrough uses the Visual Studio unit testing framework. For information about how to add another unit-testing framework, see Walkthrough: Creating a Basic MVC Project with Unit Tests in Visual Studio

To create an MVC application with unit tests

In Visual Studio, in the File menu, click New Project.
In the New Project dialog box, under Installed Templates, open the Visual C# or Visual Basic node and then select Web.
Select the ASP.NET MVC Web Application template.
Name the solution MvcContacts.
Click OK.
When the Create Unit Test Project dialog box is displayed, make sure Yes, create a unit test project is selected, and then click OK.

Visual Studio creates a solution that contains two projects, one named MvcContacts and one named MvcContacts.Tests.
On the Test menu, click Run, and then click All Tests in Solution.

The results are displayed in the Test Results window. The tests pass.
In the MvcContacts.Tests project, open and examine the account controller test class (MvcContacts\MvcContacts.Tests\Controllers\AccountControllerTest) and the account controller model class (MvcContacts\Models\AccountModels).

These classes provide a good introduction to how to create mock interfaces and to TDD. Mocking is the process of creating simple substitute (mock) objects for the dependencies in a class so you can test the class without the dependencies. To test interfaces, you typically create a mock class that implements the interface you want to test. For example, the MockMembershipService class in the account controller test class implements the IMembershipService interface to mock members that are part of membership classes, such as the ValidateUser, CreateUser, and ChangePassword methods. The MockMembershipService class enables you to test the action methods that create user accounts, validate user registration information, and change a user's password without having to instantiate a membership class like Membership.

Creating a Database Model

This walkthrough uses an Entity Data model (EDM) that is created from the Contact database that is included in the downloadable sample project. (You must download the project in order to get the Contact.mdf file. For more information, see the Prerequisites section earlier in this walkthrough.)

To create the database model

In Solution Explorer, right-click the App_Data folder of the MvcContacts project, click Add, and then click Existing Item.

The Add Existing Item dialog box is displayed.
Navigate to the folder that contains the Contact.mdf file, select the Contact.mdf file, and then click Add.
In Solution Explorer, right-click the MvcContacts project, click Add, and then click New Item.

The Add New Item dialog box is displayed.
Under Installed Templates, open the Visual C# or Visual Basic node, select Data, and then select the ADO.NET Entity Data Model template.
In the Name box enter, ContactModel and then click Add.

The Entity Data Model Wizard window is displayed.
Under What should the model contain, select Generate from database and then click Next.
Under Which data connection should your application use to connect to the database?, select Contact.mdf.
Make sure that the Save entity connection settings in Web.config as check box is selected. You can leave the default connection string name.
Click Next.

The wizard displays a page where you can specify what database objects you want to include in your model.
Select the Tables node to select the Contacts table. You can leave the default model namespace.
Click Finish.

The ADO.NET Entity Data Model Designer is displayed. Close the designer.

Adding Model Metadata

In this section, you will add the contact metadata. The contact class metadata will not be used in unit tests. However, it makes the sample more complete because it provides automated client-side and server-side data validation.

To add model metadata

In the MvcContacts\Models folder, create a new class file named ContactMD.

In this file, you'll add a class (ContactMD) that will contain the metadata for the Contact entity object that is part of the data model that you are using for this walkthrough.

Replace the code in the file with the following code:

Imports System.ComponentModel.DataAnnotations

Public Class ContactMD

    <ScaffoldColumn(False)>
    Public Property Id() As Object
    <Required()>
    Public Property FirstName() As Object
    <Required()>
    Public Property LastName() As Object
    <RegularExpression("^\d{3}-?\d{3}-?\d{4}$")>
    Public Property Phone() As Object

    <Required()>
    <DataType(DataType.EmailAddress)>
    <RegularExpression("^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$")>
    Public Property Email() As Object

End Class

using System.ComponentModel.DataAnnotations;

namespace MvcContacts.Models {
    [MetadataType(typeof(ContactMD))]
    public partial class Contact {
        public class ContactMD {
            [ScaffoldColumn(false)]
            public object Id { get; set; }
            [Required()]
            public object FirstName { get; set; }
            [Required()]
            public object LastName { get; set; }
            [RegularExpression(@"^\d{3}-?\d{3}-?\d{4}$")]
            public object Phone { get; set; }
            [Required()]
            [DataType(DataType.EmailAddress)]
            [RegularExpression(@"^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$")]
            public object Email { get; set; }
        }
    }
}

Adding a Repository

A best practice in MVC is not to include Entity Data Model (EDM) or any other data-access framework code inside your controller. Instead, you should use the repository pattern. The repository sits between the application and the data store. A repository separates the business logic from interactions with the underlying data base and focuses your data access in one area, making it easier to create and maintain.

The repository returns objects from the domain model. For simple models, such as the model that you work with in this walkthrough, the objects returned from the EDM, LINQ to SQL, and other data models qualify as domain objects.

For more complex applications, a mapping layer might be required. A mapping layer is not necessarily inefficient. LINQ providers can create efficient queries to the back-end data store (that is, they can query using a minimal number of intermediate objects).

The repository should not require knowledge of EDM, LINQ to SQL, or any other data model you are working with. (Although LINQ is not covered in this walkthrough, using LINQ as the querying abstraction means you can hide the data storage mechanism. For example, this lets you use SQL Server for production and LINQ to Objects over in-memory collections for testing.)

Testing the action methods in a controller that directly access the EDM requires a connection to a database, because the action methods are dependent on the EDM (which is dependent on a database). The following code shows a MVC controller that uses the Contact entity of the EDM directly, and it provides a simple example of why mixing database calls in action methods makes the action method difficult to test. For example, unit tests that edit and delete data change the state of the database. This requires each pass of the unit tests to have a clean database setup. Additionally, database calls are very expensive, whereas unit tests should be lightweight so they can be run frequently while you are developing your application.

Public Class NotTDDController
    Inherits System.Web.Mvc.Controller

    Private _db As New ContactEntities()

    Public Function Index() As ActionResult
        Dim dn = _db.Contacts
        Return View(dn)
    End Function

    Public Function Edit(ByVal id As Integer) As ActionResult
        Dim prd As Contact = _db.Contacts.FirstOrDefault(Function(d) d.Id = id)
        Return View(prd)
    End Function

    <HttpPost()>
    Public Function Edit(ByVal id As Integer, ByVal collection As FormCollection) As ActionResult
        Dim prd As Contact = _db.Contacts.FirstOrDefault(Function(d) d.Id = id)
        UpdateModel(prd)
        _db.SaveChanges()
        Return RedirectToAction("Index")
    End Function
End Class

public class NotTDDController : Controller {

    ContactEntities _db = new ContactEntities();

    public ActionResult Index() {
        var dn = _db.Contacts;
        return View(dn);
    }

    public ActionResult Edit(int id) {
        Contact prd = _db.Contacts.FirstOrDefault(d => d.Id == id);
        return View(prd);
    }

    [HttpPost]
    public ActionResult Edit(int id, FormCollection collection) {
        Contact prd = _db.Contacts.FirstOrDefault(d => d.Id == id);
        UpdateModel(prd);
        _db.SaveChanges();
        return RedirectToAction("Index");
    }
}

The repository pattern has the following benefits:

It provides a substitution point for the unit tests. You can easily test business logic without a database and other external dependencies.
Duplicated queries and data-access patterns can be removed and refactored into the repository.
Controller methods can use strongly typed parameters, which means the compiler finds data-typing errors each time you compile instead of relying of finding data-typing errors at run time when testing.
Data access is centralized, which provides the following benefits:
- Greater separation of concerns (SoC), another tenet of MVC, which increases maintainability and readability.
- Simplified implementation of centralized data caching.
- A more flexible and less coupled architecture that can be adapted as the overall design of the application evolves.
Behavior can be associated with related data. For example, you can calculate fields or enforce complex relationships or business rules between the data elements within an entity.
A domain model can be applied in order to simplify complex business logic.

Using the repository pattern with MVC and TDD typically requires you to create an interface for your data-access class. The repository interface will make it easy to inject a mock repository when you unit test our controller methods.

In this section, you will add a contact repository, which is a class that is used to save the contacts in a database. You will also add an interface for the contact repository.

To add a repository

In the MvcContacts\Models folder, create a class file and add a class named IContactRepository.

The IContactRepository class will contain the interface for the repository object.

Replace the code in the class file with the following code:

Public Interface IContactRepository
    Sub CreateNewContact(ByVal contactToCreate As Contact)
    Sub DeleteContact(ByVal id As Integer)
    Function GetContactByID(ByVal id As Integer) As Contact
    Function GetAllContacts() As IEnumerable(Of Contact)
    Function SaveChanges() As Integer
End Interface

using System;
using System.Collections.Generic;

namespace MvcContacts.Models {
    public interface IContactRepository {
        void CreateNewContact(Contact contactToCreate);
        void DeleteContact(int id);
        Contact GetContactByID(int id);
        IEnumerable<Contact> GetAllContacts();
        int SaveChanges();

    }
}

In the MvcContacts\Models folder, create a new class named EntityContactManagerRepository.

The EntityContactManagerRepository class will implement the IContactRepository interface for the repository object.

Replace the code in the EntityContactManagerRepository class with the following code:


Public Class EF_ContactRepository
    Implements IContactRepository

    Private _db As New ContactEntities()

    Public Function GetContactByID(ByVal id As Integer) As Contact Implements IContactRepository.GetContactByID
        Return _db.Contacts.FirstOrDefault(Function(d) d.Id = id)
    End Function

    Public Function GetAllContacts() As IEnumerable(Of Contact) Implements IContactRepository.GetAllContacts
        Return _db.Contacts.ToList()
    End Function

    Public Sub CreateNewContact(ByVal contactToCreate As Contact) Implements IContactRepository.CreateNewContact
        _db.AddToContacts(contactToCreate)
        _db.SaveChanges()
        '   return contactToCreate;
    End Sub

    Public Function SaveChanges() As Integer Implements IContactRepository.SaveChanges
        Return _db.SaveChanges()
    End Function

    Public Sub DeleteContact(ByVal id As Integer) Implements IContactRepository.DeleteContact
        Dim conToDel = GetContactByID(id)
        _db.Contacts.DeleteObject(conToDel)
        _db.SaveChanges()
    End Sub

End Class

using System.Collections.Generic;
using System.Linq;

namespace MvcContacts.Models {
    public class EF_ContactRepository : MvcContacts.Models.IContactRepository {

        private ContactEntities _db = new ContactEntities();

        public Contact GetContactByID(int id) {
            return _db.Contacts.FirstOrDefault(d => d.Id == id);
        }

        public IEnumerable<Contact> GetAllContacts() {
            return _db.Contacts.ToList();
        }

        public void CreateNewContact(Contact contactToCreate) {
            _db.AddToContacts(contactToCreate);
            _db.SaveChanges();
         //   return contactToCreate;
        }

        public int SaveChanges() {
            return _db.SaveChanges();
        }

        public void DeleteContact(int id) {
            var conToDel = GetContactByID(id);
            _db.Contacts.DeleteObject(conToDel);
            _db.SaveChanges();
        }

    }
}

Creating Tests to Drive Design

In this section, you will add a mock implementation of the repository, add unit tests, and implement the application functionality from the unit tests.

To implement the in-memory repository

In the MvcContacts.Tests project, create a Models folder.
In the MvcContacts.Tests\Models folder, create a new class named InMemoryContactRepository.

The InMemoryContactRepository class will implement the IContactRepository interface that you created previously and have a simple repository for driving the application design.

Replace the code in the InMemoryContactRepository class with the following code:


Class InMemoryContactRepository
    Implements IContactRepository

    Private _db As New List(Of Contact)()
    Public Property ExceptionToThrow() As Exception

    Public Function SaveChanges() As Integer Implements IContactRepository.SaveChanges
        Return 1
    End Function

    Public Sub Add(ByVal contactToAdd As Contact)
        _db.Add(contactToAdd)
    End Sub

    Public Function GetContactByID(ByVal id As Integer) As Contact Implements IContactRepository.GetContactByID
        Return _db.FirstOrDefault(Function(d) d.Id = id)
    End Function

    Public Sub CreateNewContact(ByVal contactToCreate As Contact) Implements IContactRepository.CreateNewContact
        If ExceptionToThrow IsNot Nothing Then
            Throw ExceptionToThrow
        End If

        _db.Add(contactToCreate)
    End Sub


    Public Function GetAllContacts() As IEnumerable(Of Contact) Implements IContactRepository.GetAllContacts
        Return _db.ToList()
    End Function


    Public Sub DeleteContact(ByVal id As Integer) Implements IContactRepository.DeleteContact
        _db.Remove(GetContactByID(id))
    End Sub

End Class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using MvcContacts.Models;

namespace MvcContacts.Tests.Models {
    class InMemoryContactRepository : MvcContacts.Models.IContactRepository {
        private List<Contact> _db = new List<Contact>();

        public Exception ExceptionToThrow { get; set; }
        //public List<Contact> Items { get; set; }

        public void SaveChanges(Contact contactToUpdate) {

            foreach (Contact contact in _db) {
                if (contact.Id == contactToUpdate.Id) {
                    _db.Remove(contact);
                    _db.Add(contactToUpdate);
                    break;
                }
            }
        }

        public void Add(Contact contactToAdd) {
            _db.Add(contactToAdd);
        }

        public Contact GetContactByID(int id) {
            return _db.FirstOrDefault(d => d.Id == id);
        }

        public void CreateNewContact(Contact contactToCreate) {
            if (ExceptionToThrow != null)
                throw ExceptionToThrow;

            _db.Add(contactToCreate);
           // return contactToCreate;
        }

        public int SaveChanges() {
            return 1;
        }

        public IEnumerable<Contact> GetAllContacts() {
            return _db.ToList();
        }


        public void DeleteContact(int id) {
            _db.Remove(GetContactByID(id));
        }

    }
}

To add test support

In the MvcContacts project, open the Controllers\HomeController.cs file. Replace the code in the Controllers\HomeController.cs file with the following code:

using System;
using System.Web.Mvc;
using MvcContacts.Models;

namespace MvcContacts.Controllers {
    [HandleError]
    public class HomeController : Controller {
        IContactRepository _repository;
        public HomeController() : this(new EF_ContactRepository()) { }
        public HomeController(IContactRepository repository) {
            _repository = repository;
        }
        public ViewResult Index() {
            throw new NotImplementedException();
        }
    }
}

<HandleError()> _
Public Class HomeController
    Inherits System.Web.Mvc.Controller

    Private _repository As IContactRepository

    Public Sub New()
        Me.New(New EF_ContactRepository())
    End Sub

    Public Sub New(ByVal repository As IContactRepository)
        _repository = repository
    End Sub

    Public Function Index() As ViewResult
        Throw New NotImplementedException()
        Return View()
    End Function
End Class

This class contains two constructors. One is a parameterless constructor. The other takes a parameter of type IContactRepository; this constructor will be used by the unit tests to pass in the mock repository. The parameterless constructor creates an instance of the EF_ContactRepository class and is called by the MVC pipeline when an action method in the controller is invoked.

Close the HomeController file.

In the MvcContacts.Test project, open the Controllers\HomeControllerTest file and replace the code in the file with the following code:

using System.Web.Mvc;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using MvcContacts.Controllers;

using MvcContacts.Models;
using MvcContacts.Tests.Models;
using System.Web;
using System.Web.Routing;
using System.Security.Principal;

namespace MvcContacts.Tests.Controllers {
    [TestClass]
    public class HomeControllerTest {

        Contact GetContact() {
            return GetContact(1, "Janet", "Gates");
        }

        Contact GetContact(int id, string fName, string lName) {
            return new Contact
            {
                Id = id,
                FirstName = fName,
                LastName = lName,
                Phone = "710-555-0173",
                Email = "janet1@adventure-works.com"
            };
        }

        private static HomeController GetHomeController(IContactRepository repository) {
            HomeController controller = new HomeController(repository);

            controller.ControllerContext = new ControllerContext()
            {
                Controller = controller,
                RequestContext = new RequestContext(new MockHttpContext(), new RouteData())
            };
            return controller;
        }


        private class MockHttpContext : HttpContextBase {
            private readonly IPrincipal _user = new GenericPrincipal(
                     new GenericIdentity("someUser"), null /* roles */);

            public override IPrincipal User {
                get {
                    return _user;
                }
                set {
                    base.User = value;
                }
            }
        }
    }
}

Imports System
Imports System.Security
Imports System.Security.Principal
Imports System.Web
Imports System.Web.Mvc
Imports System.Web.Routing
Imports System.Web.Security
Imports Microsoft.VisualStudio.TestTools.UnitTesting
Imports MvcContacts

<TestClass()> Public Class HomeControllerTest




   <TestMethod()>
    Public Sub Index_Get_AsksForIndexView()
        ' Arrange
        Dim controller = GetHomeController(New InMemoryContactRepository())
        ' Act
        Dim result As ViewResult = controller.Index()
        ' Assert
        Assert.AreEqual("Index", result.ViewName)
    End Sub
    ' </snippet8>

    Private Function GetContactID_1() As Contact
        Return GetContactNamed(1, "Janet", "Gates")
    End Function

    Private Function GetContactNamed(ByVal id As Integer, ByVal fName As String, ByVal lName As String) As Contact
        Return New Contact With {.Id = id,
                                 .FirstName = fName,
                                 .LastName = lName,
                                 .Phone = "710-555-0173",
                                 .Email = "janet1@adventure-works.com"}

    End Function

    Private Shared Function GetHomeController(ByVal repository As IContactRepository) As HomeController
        Dim controller As New HomeController(repository)

        controller.ControllerContext = New ControllerContext() With
                                       {.Controller = controller,
                                         .RequestContext = New RequestContext(New MockHttpContext(),
                                        New RouteData())}
        Return controller
    End Function

    Private Class MockHttpContext
        Inherits HttpContextBase

        Private ReadOnly _user As IPrincipal = New GenericPrincipal(New GenericIdentity("someUser"), Nothing)

        Public Overrides Property User() As IPrincipal
            Get
                Return _user
            End Get
            Set(ByVal value As System.Security.Principal.IPrincipal)
                MyBase.User = value
            End Set
        End Property
    End Class

End Class

The code in the preceding example contains two method overloads that get a contact (GetContact) and a method to get the HomeController object. The unit tests will call methods in the HomeController. The code also contains a class to mock the HttpContext object. The MockHttpContext class used in this sample is a simplified version of the one found in the AcountControllerTest class file created when you made a new MVC project with unit tests.

Adding Tests

One of the tenets of TDD with MVC is that each test should drive a specific requirement in an action method. The test should not verify database or other components (although these components should be tested in the data access unit tests and in integration testing). Another goal is that test names should be very descriptive; short general names like Creat_Post_Test1 will make it more difficult to understand the test when you have hundreds of tests.

In this part of the walkthrough, you will assume the design calls for the default method of the Home controller to return a list of contacts. The default method for the controller is Index, so the first test will verify that the controller returns the index view. When you made changes to the Index method earlier in this walkthrough, you changed it to return a ViewResult object, not the more general ActionResult object. When you know a method will always return a ViewResult object, you can simplify the unit tests by returning a ViewResult object from the controller method. When you return a ViewResult object, the unit test does not have to cast the typical ActionResult object to a ViewResult object as part of the test, which results in simpler and more readable tests

To add the first test

In the HomeControllerTest class, add a unit test named Index_Get_AsksForIndexView that verifies that the Index method returns a view named Index.

The following example shows the completed unit test.

<TestMethod()>
Public Sub Index_Get_AsksForIndexView()
    ' Arrange
    Dim controller = GetHomeController(New InMemoryContactRepository())
    ' Act
    Dim result As ViewResult = controller.Index()
    ' Assert
    Assert.AreEqual("Index", result.ViewName)
End Sub

[TestMethod]
public void Index_Get_AsksForIndexView() {
    // Arrange
    var controller = GetHomeController(new InMemoryContactRepository());
    // Act
    ViewResult result = controller.Index();
    // Assert
    Assert.AreEqual("Index", result.ViewName);
}

On the Test menu, click Run, and then click All Tests in Solution.

The results are displayed in the Test Results window. As expected, the Index_Get_AsksForIndexView unit test fails.
Implement the following Index method of the HomeController class in order to return a list of all the contacts.
```
public ViewResult Index() {
            return View("Index", _repository.ListContacts());
        }
```
In the spirit of TDD, you write just enough code to satisfy the design test.
Run the tests. This time the Index_Get_AsksForIndexView unit test passes.

Creating a Test for Retrieving Contacts

In this section you will verify that you can retrieve all the contacts. You do not want to create unit tests that test data access. Verifying your application can access the database and retrieve contacts is important, but that is an integration test, not a TDD unit test.

To add a test for retrieving contacts

Create a test that adds two contacts to the in-memory repository in the HomeControllerTest class and then verifies that they are contained in the ViewData Model object that is contained in the Index view.

The following example shows the completed test.

<TestMethod()>
Public Sub Index_Get_RetrievesAllContactsFromRepository()
    ' Arrange
    Dim contact1 As Contact = GetContactNamed(1, "Orlando", "Gee")
    Dim contact2 As Contact = GetContactNamed(2, "Keith", "Harris")
    Dim repository As New InMemoryContactRepository()
    repository.Add(contact1)
    repository.Add(contact2)
    Dim controller = GetHomeController(repository)

    ' Act
    Dim result = controller.Index()

    ' Assert
    Dim model = CType(result.ViewData.Model, IEnumerable(Of Contact))
    CollectionAssert.Contains(model.ToList(), contact1)
    CollectionAssert.Contains(model.ToList(), contact1)
End Sub

[TestMethod]
public void Index_Get_RetrievesAllContactsFromRepository() {
    // Arrange
    Contact contact1 = GetContactNamed(1, "Orlando", "Gee");
    Contact contact2 = GetContactNamed(2, "Keith", "Harris");
    InMemoryContactRepository repository = new InMemoryContactRepository();
    repository.Add(contact1);
    repository.Add(contact2);
    var controller = GetHomeController(repository);

    // Act
    var result = controller.Index();

    // Assert
    var model = (IEnumerable<Contact>)result.ViewData.Model;
    CollectionAssert.Contains(model.ToList(), contact1);
    CollectionAssert.Contains(model.ToList(), contact1);
}

Creating a Test for Creating a Contact

You will now test the process of creating a new contact. The first test verifies that an HTTP POST operation has completed successfully and invoked the Create method using data that deliberately contains model errors. The result will not add a new contact but instead returns the HTTP GET Create view that contains the fields you have entered and the model errors. Running a unit test on a controller does not execute the MVC pipeline or model-binding process. Therefore, the model error would not be caught during the binding process. To account for this, the test adds a mock error.

To add a test for creating a contact

Add the following test to the project:

<TestMethod()>
Public Sub Create_Post_ReturnsViewIfModelStateIsNotValid()
    ' Arrange
    Dim controller As HomeController = GetHomeController(New InMemoryContactRepository())
    ' Simply executing a method during a unit test does just that - executes a method, and no more. 
    ' The MVC pipeline doesn't run, so binding and validation don't run.
    controller.ModelState.AddModelError("", "mock error message")
    Dim model As Contact = GetContactNamed(1, "", "")

    ' Act
    Dim result = CType(controller.Create(model), ViewResult)

    ' Assert
    Assert.AreEqual("Create", result.ViewName)
End Sub

[TestMethod]
public void Create_Post_ReturnsViewIfModelStateIsNotValid() {
    // Arrange
    HomeController controller = GetHomeController(new InMemoryContactRepository());
    // Simply executing a method during a unit test does just that - executes a method, and no more. 
    // The MVC pipeline doesn't run, so binding and validation don't run.
    controller.ModelState.AddModelError("", "mock error message");
    Contact model = GetContactNamed(1, "", "");

    // Act
    var result = (ViewResult)controller.Create(model);

    // Assert
    Assert.AreEqual("Create", result.ViewName);
}

The code shows how an attempt to add a contact that contains model errors returns the HTTP GET Create view.

Add the following test:

<TestMethod()>
Public Sub Create_Post_PutsValidContactIntoRepository()
    ' Arrange
    Dim repository As New InMemoryContactRepository()
    Dim controller As HomeController = GetHomeController(repository)
    Dim contact_Renamed As Contact = GetContactID_1()

    ' Act
    controller.Create(contact_Renamed)

    ' Assert
    Dim contacts As IEnumerable(Of Contact) = repository.GetAllContacts()
    Assert.IsTrue(contacts.Contains(contact_Renamed))
End Sub

[TestMethod]
public void Create_Post_PutsValidContactIntoRepository() {
    // Arrange
    InMemoryContactRepository repository = new InMemoryContactRepository();
    HomeController controller = GetHomeController(repository);
    Contact contact = GetContactID_1();

    // Act
    controller.Create(contact);

    // Assert
    IEnumerable<Contact> contacts = repository.GetAllContacts();
    Assert.IsTrue(contacts.Contains(contact));
}

The code shows how to verify that an HTTP POST to the Create method adds a valid contact to the repository.

A test that is often overlooked is to verify that methods correctly handle exceptions. The InMemoryContactRepository class lets you set a mock exception, simulating an exception that a database would raise when a constraint or other violation occurred. Many database exceptions cannot be caught with model validation, so it is important to verify exception handling code works correctly. The following example shows how to do this.

<TestMethod()>
Public Sub Create_Post_ReturnsViewIfRepositoryThrowsException()
    ' Arrange
    Dim repository As New InMemoryContactRepository()
    Dim exception_Renamed As New Exception()
    repository.ExceptionToThrow = exception_Renamed
    Dim controller As HomeController = GetHomeController(repository)
    Dim model As Contact = GetContactID_1()

    ' Act
    Dim result = CType(controller.Create(model), ViewResult)

    ' Assert
    Assert.AreEqual("Create", result.ViewName)
    Dim modelState_Renamed As ModelState = result.ViewData.ModelState("")
    Assert.IsNotNull(modelState_Renamed)
    Assert.IsTrue(modelState_Renamed.Errors.Any())
    Assert.AreEqual(exception_Renamed, modelState_Renamed.Errors(0).Exception)
End Sub

[TestMethod]
public void Create_Post_ReturnsViewIfRepositoryThrowsException() {
    // Arrange
    InMemoryContactRepository repository = new InMemoryContactRepository();
    Exception exception = new Exception();
    repository.ExceptionToThrow = exception;
    HomeController controller = GetHomeController(repository);
    Contact model = GetContactID_1();

    // Act
    var result = (ViewResult)controller.Create(model);

    // Assert
    Assert.AreEqual("Create", result.ViewName);
    ModelState modelState = result.ViewData.ModelState[""];
    Assert.IsNotNull(modelState);
    Assert.IsTrue(modelState.Errors.Any());
    Assert.AreEqual(exception, modelState.Errors[0].Exception);
}

Next Steps

The downloadable sample includes more tests that are not detailed here. To learn more about how to use mock objects and how to use TDD methodology with MVC projects, review the additional tests, and write tests for the Delete and Edit methods.