Razor Pages unit tests in ASP.NET Core

ASP.NET Core supports unit tests of Razor Pages apps. Tests of the data access layer (DAL) and page models help ensure:

• Parts of a Razor Pages app work independently and together as a unit during app construction.
• Classes and methods have limited scopes of responsibility.
• Additional documentation exists on how the app should behave.
• Regressions, which are errors brought about by updates to the code, are found during automated building and deployment.

This topic assumes that you have a basic understanding of Razor Pages apps and unit tests. If you're unfamiliar with Razor Pages apps or test concepts, see the following topics:

• Introduction to Razor Pages in ASP.NET Core
• Tutorial: Get started with Razor Pages in ASP.NET Core
• Unit testing C# in .NET Core using dotnet test and xUnit

View or download sample code (how to download)

The sample project is composed of two apps:

App	Project folder	Description
Message app	src/RazorPagesTestSample	Allows a user to add a message, delete one message, delete all messages, and analyze messages (find the average number of words per message).
Test app	tests/RazorPagesTestSample.Tests	Used to unit test the DAL and Index page model of the message app.

The tests can be run using the built-in test features of an IDE, such as Visual Studio. If using Visual Studio Code or the command line, execute the following command at a command prompt in the tests/RazorPagesTestSample.Tests folder:

dotnet test

Message app organization

The message app is a Razor Pages message system with the following characteristics:

• The Index page of the app (Pages/Index.cshtml and Pages/Index.cshtml.cs) provides a UI and page model methods to control the addition, deletion, and analysis of messages (find the average number of words per message).
• A message is described by the Message class (Data/Message.cs) with two properties: Id (key) and Text (message). The Text property is required and limited to 200 characters.
• Messages are stored using Entity Framework's in-memory database†.
• The app contains a DAL in its database context class, AppDbContext (Data/AppDbContext.cs). The DAL methods are marked virtual, which allows mocking the methods for use in the tests.
• If the database is empty on app startup, the message store is initialized with three messages. These seeded messages are also used in tests.

†The EF topic, Test with InMemory, explains how to use an in-memory database for tests with MSTest. This topic uses the xUnit test framework. Test concepts and test implementations across different test frameworks are similar but not identical.

Although the sample app doesn't use the repository pattern and isn't an effective example of the Unit of Work (UoW) pattern, Razor Pages supports these patterns of development. For more information, see Designing the infrastructure persistence layer and Test controller logic in ASP.NET Core (the sample implements the repository pattern).

Test app organization

The test app is a console app inside the tests/RazorPagesTestSample.Tests folder.

Test app folder	Description
UnitTests	DataAccessLayerTest.cs contains the unit tests for the DAL. IndexPageTests.cs contains the unit tests for the Index page model.
Utilities	Contains the TestDbContextOptions method used to create new database context options for each DAL unit test so that the database is reset to its baseline condition for each test.

The test framework is xUnit. The object mocking framework is Moq.

Unit tests of the data access layer (DAL)

The message app has a DAL with four methods contained in the AppDbContext class (src/RazorPagesTestSample/Data/AppDbContext.cs). Each method has one or two unit tests in the test app.

DAL method	Function
GetMessagesAsync	Obtains a List<Message> from the database sorted by the Text property.
AddMessageAsync	Adds a Message to the database.
DeleteAllMessagesAsync	Deletes all Message entries from the database.
DeleteMessageAsync	Deletes a single Message from the database by Id.

Unit tests of the DAL require DbContextOptions when creating a new AppDbContext for each test. One approach to creating the DbContextOptions for each test is to use a DbContextOptionsBuilder:

var optionsBuilder = new DbContextOptionsBuilder<AppDbContext>()
    .UseInMemoryDatabase("InMemoryDb");

using (var db = new AppDbContext(optionsBuilder.Options))
{
    // Use the db here in the unit test.
}

The problem with this approach is that each test receives the database in whatever state the previous test left it. This can be problematic when trying to write atomic unit tests that don't interfere with each other. To force the AppDbContext to use a new database context for each test, supply a DbContextOptions instance that's based on a new service provider. The test app shows how to do this using its Utilities class method TestDbContextOptions (tests/RazorPagesTestSample.Tests/Utilities/Utilities.cs):

public static DbContextOptions<AppDbContext> TestDbContextOptions()
{
    // Create a new service provider to create a new in-memory database.
    var serviceProvider = new ServiceCollection()
        .AddEntityFrameworkInMemoryDatabase()
        .BuildServiceProvider();

    // Create a new options instance using an in-memory database and 
    // IServiceProvider that the context should resolve all of its 
    // services from.
    var builder = new DbContextOptionsBuilder<AppDbContext>()
        .UseInMemoryDatabase("InMemoryDb")
        .UseInternalServiceProvider(serviceProvider);

    return builder.Options;
}

Using the DbContextOptions in the DAL unit tests allows each test to run atomically with a fresh database instance:

using (var db = new AppDbContext(Utilities.TestDbContextOptions()))
{
    // Use the db here in the unit test.
}

Each test method in the DataAccessLayerTest class (UnitTests/DataAccessLayerTest.cs) follows a similar Arrange-Act-Assert pattern:

1. Arrange: The database is configured for the test and/or the expected outcome is defined.
2. Act: The test is executed.
3. Assert: Assertions are made to determine if the test result is a success.

For example, the DeleteMessageAsync method is responsible for removing a single message identified by its Id (src/RazorPagesTestSample/Data/AppDbContext.cs):

public async virtual Task DeleteMessageAsync(int id)
{
    var message = await Messages.FindAsync(id);

    if (message != null)
    {
        Messages.Remove(message);
        await SaveChangesAsync();
    }
}

There are two tests for this method. One test checks that the method deletes a message when the message is present in the database. The other method tests that the database doesn't change if the message Id for deletion doesn't exist. The DeleteMessageAsync_MessageIsDeleted_WhenMessageIsFound method is shown below:

[Fact]
public async Task DeleteMessageAsync_MessageIsDeleted_WhenMessageIsFound()
{
    using (var db = new AppDbContext(Utilities.TestDbContextOptions()))
    {
        // Arrange
        var seedMessages = AppDbContext.GetSeedingMessages();
        await db.AddRangeAsync(seedMessages);
        await db.SaveChangesAsync();
        var recId = 1;
        var expectedMessages = 
            seedMessages.Where(message => message.Id != recId).ToList();

        // Act
        await db.DeleteMessageAsync(recId);

        // Assert
        var actualMessages = await db.Messages.AsNoTracking().ToListAsync();
        Assert.Equal(
            expectedMessages.OrderBy(m => m.Id).Select(m => m.Text), 
            actualMessages.OrderBy(m => m.Id).Select(m => m.Text));
    }
}

First, the method performs the Arrange step, where preparation for the Act step takes place. The seeding messages are obtained and held in seedMessages. The seeding messages are saved into the database. The message with an Id of 1 is set for deletion. When the DeleteMessageAsync method is executed, the expected messages should have all of the messages except for the one with an Id of 1. The expectedMessages variable represents this expected outcome.

// Arrange
var seedMessages = AppDbContext.GetSeedingMessages();
await db.AddRangeAsync(seedMessages);
await db.SaveChangesAsync();
var recId = 1;
var expectedMessages = 
    seedMessages.Where(message => message.Id != recId).ToList();

The method acts: The DeleteMessageAsync method is executed passing in the recId of 1:

// Act
await db.DeleteMessageAsync(recId);

Finally, the method obtains the Messages from the context and compares it to the expectedMessages asserting that the two are equal:

// Assert
var actualMessages = await db.Messages.AsNoTracking().ToListAsync();
Assert.Equal(
    expectedMessages.OrderBy(m => m.Id).Select(m => m.Text), 
    actualMessages.OrderBy(m => m.Id).Select(m => m.Text));

In order to compare that the two List<Message> are the same:

• The messages are ordered by Id.
• Message pairs are compared on the Text property.

A similar test method, DeleteMessageAsync_NoMessageIsDeleted_WhenMessageIsNotFound checks the result of attempting to delete a message that doesn't exist. In this case, the expected messages in the database should be equal to the actual messages after the DeleteMessageAsync method is executed. There should be no change to the database's content:

[Fact]
public async Task DeleteMessageAsync_NoMessageIsDeleted_WhenMessageIsNotFound()
{
    using (var db = new AppDbContext(Utilities.TestDbContextOptions()))
    {
        // Arrange
        var expectedMessages = AppDbContext.GetSeedingMessages();
        await db.AddRangeAsync(expectedMessages);
        await db.SaveChangesAsync();
        var recId = 4;

        // Act
        try
        {
            await db.DeleteMessageAsync(recId);
        }
        catch
        {
            // recId doesn't exist
        }

        // Assert
        var actualMessages = await db.Messages.AsNoTracking().ToListAsync();
        Assert.Equal(
            expectedMessages.OrderBy(m => m.Id).Select(m => m.Text), 
            actualMessages.OrderBy(m => m.Id).Select(m => m.Text));
    }
}

Unit tests of the page model methods

Another set of unit tests is responsible for tests of page model methods. In the message app, the Index page models are found in the IndexModel class in src/RazorPagesTestSample/Pages/Index.cshtml.cs.

Page model method	Function
OnGetAsync	Obtains the messages from the DAL for the UI using the GetMessagesAsync method.
OnPostAddMessageAsync	If the ModelState is valid, calls AddMessageAsync to add a message to the database.
OnPostDeleteAllMessagesAsync	Calls DeleteAllMessagesAsync to delete all of the messages in the database.
OnPostDeleteMessageAsync	Executes DeleteMessageAsync to delete a message with the Id specified.
OnPostAnalyzeMessagesAsync	If one or more messages are in the database, calculates the average number of words per message.

The page model methods are tested using seven tests in the IndexPageTests class (tests/RazorPagesTestSample.Tests/UnitTests/IndexPageTests.cs). The tests use the familiar Arrange-Assert-Act pattern. These tests focus on:

• Determining if the methods follow the correct behavior when the ModelState is invalid.
• Confirming the methods produce the correct IActionResult.
• Checking that property value assignments are made correctly.

This group of tests often mock the methods of the DAL to produce expected data for the Act step where a page model method is executed. For example, the GetMessagesAsync method of the AppDbContext is mocked to produce output. When a page model method executes this method, the mock returns the result. The data doesn't come from the database. This creates predictable, reliable test conditions for using the DAL in the page model tests.

The OnGetAsync_PopulatesThePageModel_WithAListOfMessages test shows how the GetMessagesAsync method is mocked for the page model:

var mockAppDbContext = new Mock<AppDbContext>(optionsBuilder.Options);
var expectedMessages = AppDbContext.GetSeedingMessages();
mockAppDbContext.Setup(
    db => db.GetMessagesAsync()).Returns(Task.FromResult(expectedMessages));
var pageModel = new IndexModel(mockAppDbContext.Object);

When the OnGetAsync method is executed in the Act step, it calls the page model's GetMessagesAsync method.

Unit test Act step (tests/RazorPagesTestSample.Tests/UnitTests/IndexPageTests.cs):

// Act
await pageModel.OnGetAsync();

IndexPage page model's OnGetAsync method (src/RazorPagesTestSample/Pages/Index.cshtml.cs):

public async Task OnGetAsync()
{
    Messages = await _db.GetMessagesAsync();
}

The GetMessagesAsync method in the DAL doesn't return the result for this method call. The mocked version of the method returns the result.

In the Assert step, the actual messages (actualMessages) are assigned from the Messages property of the page model. A type check is also performed when the messages are assigned. The expected and actual messages are compared by their Text properties. The test asserts that the two List<Message> instances contain the same messages.

// Assert
var actualMessages = Assert.IsAssignableFrom<List<Message>>(pageModel.Messages);
Assert.Equal(
    expectedMessages.OrderBy(m => m.Id).Select(m => m.Text), 
    actualMessages.OrderBy(m => m.Id).Select(m => m.Text));

Other tests in this group create page model objects that include the DefaultHttpContext, the ModelStateDictionary, an ActionContext to establish the PageContext, a ViewDataDictionary, and a PageContext. These are useful in conducting tests. For example, the message app establishes a ModelState error with AddModelError to check that a valid PageResult is returned when OnPostAddMessageAsync is executed:

[Fact]
public async Task OnPostAddMessageAsync_ReturnsAPageResult_WhenModelStateIsInvalid()
{
    // Arrange
    var optionsBuilder = new DbContextOptionsBuilder<AppDbContext>()
        .UseInMemoryDatabase("InMemoryDb");
    var mockAppDbContext = new Mock<AppDbContext>(optionsBuilder.Options);
    var expectedMessages = AppDbContext.GetSeedingMessages();
    mockAppDbContext.Setup(db => db.GetMessagesAsync()).Returns(Task.FromResult(expectedMessages));
    var httpContext = new DefaultHttpContext();
    var modelState = new ModelStateDictionary();
    var actionContext = new ActionContext(httpContext, new RouteData(), new PageActionDescriptor(), modelState);
    var modelMetadataProvider = new EmptyModelMetadataProvider();
    var viewData = new ViewDataDictionary(modelMetadataProvider, modelState);
    var tempData = new TempDataDictionary(httpContext, Mock.Of<ITempDataProvider>());
    var pageContext = new PageContext(actionContext)
    {
        ViewData = viewData
    };
    var pageModel = new IndexModel(mockAppDbContext.Object)
    {
        PageContext = pageContext,
        TempData = tempData,
        Url = new UrlHelper(actionContext)
    };
    pageModel.ModelState.AddModelError("Message.Text", "The Text field is required.");

    // Act
    var result = await pageModel.OnPostAddMessageAsync();

    // Assert
    Assert.IsType<PageResult>(result);
}

Additional resources

• Unit testing C# in .NET Core using dotnet test and xUnit
• Test controller logic in ASP.NET Core
• Unit Test Your Code (Visual Studio)
• Integration tests in ASP.NET Core
• xUnit.net
• Getting started with xUnit.net: Using .NET Core with the .NET SDK command line
• Moq
• Moq Quickstart