Testing with bUnit - Overview

bUnit extends other unit testing frameworks (xUnit, Nunit, MSTest, etc) for Blazor-specific unit tests.

features

includes a semantic HTML comparer so that not all possible cases must be manually tested.
supports dependency injection and passing parameters
testing user interactions and event handlers
testing IJSRuntime
testing authorization
mocking an HttpClient

simple unit test example

public void CanUpdatePiePrice() 
{
    // Arrange
    var pie = new Pie() { Name = "Sample pie", Price = 12.95M };

    // Act
    pie.Price = 20M;

    // Assert
    Assert.Equal(20M, pie.Price);
}

using bunit

process

Install the bUnit Visual Studio template
dotnet new --install bunit.template
Create a bUnit project
dotnet new bunit --framework xunit -o project-name
Add the bUnit project to your Solution
From the bUnit project, add a project reference to the main project
Start writing unit tests

writing unit tests

bUnit supports writing tests in C# (.cs) or Razor files (.razor).

razor example

Assuming this Component:
MainProject/Components/SampleComponent.razor

<h3>Inbox</h3>

@if (@MessageCount > 0)
{
    <h4>You currently have @MessageCount questions from employees!</h4>
}
else
{
    <h4>No questions from employees! All good!</h4>
}

@code
{
    [Parameter]
    public int MessageCount { get; set; }
}

Unit test for the above Component:
TestProject/SampleComponentTests.razor

@code {
    [Fact]
    public void RenderSampleComponentWithValueGreaterThanZero()
    {
        // Arrange
        // TestContext provides access to the Component
        using var ctx = new TestContext();

        // Act
        // cut = component under test
        // use the context's Render method and pass in the Component to be tested, including a test value for the MessageCount parameter:
        var cut = ctx.Render(@<SampleComponent MessageCount="3" />);

        // Assert
        // pass in the expected HTML output:
        cut.MarkupMatches("<h3>Inbox</h3><h4>You currently have 3 questions from employees!</h4>"); 
    }

    [Fact]
    public void RenderSampleComponentWithZero()
    {
        // Arrange
        using var ctx = new TestContext();

        // Act
        var cut = ctx.Render(@<SampleComponent MessageCount="0" />);

        // Assert
        cut.MarkupMatches("<h3>Inbox</h3><h4>No questions from employees! All good!</h4>"); 
    }
}

Alternatively, inherit TestContext to avoid creating one in each method:

@inherits TestContext

@code
{
    [Fact]
    public void RenderSampleComponentWithValueGreaterThanZero()
    {
        var cut = ctx.Render(@<SampleComponent MessageCount="3" />);

        cut.MarkupMatches("<h3>Inbox</h3><h4>You currently have 3 questions from employees!</h4>"); 
    }
    // ...
}

test only a part of a component

TestProject/EmployeeCardTests.razor

@using BethanysPieShopHRM.Shared.Domain

@inherits TestContext

@code 
{
    private Employee _employee;

    public EmployeeCardTests()
    {
        var jobCategory = new JobCategory { JobCategoryId = 3, JobCategoryName = "Management" };
        var country = new Country { CountryId = 1, Name = "Belgium" };

        _employee = new Employee()
        {
            MaritalStatus = MaritalStatus.Single,
            BirthDate = new DateTime(1989, 3, 11),
            City = "Brussels",
            Email = "bethany@bethanyspieshop.com",
            EmployeeId = 1,
            FirstName = "Bethany",
            LastName = "Smith",
            Gender = Gender.Female,
            PhoneNumber = "324777888978978",
            Smoker = false,
            Street = "Grote Markt 1",
            Zip = "1000",
            JobCategory = jobCategory,
            JobCategoryId = jobCategory.JobCategoryId,
            Comment = "Lorem Ipsum",
            ExitDate = null,
            JoinedDate = new DateTime(2015, 3, 1),
            Country = country,
            CountryId = country.CountryId
        };
    }

    [Fact]
    public void RenderEmployeeCardDetailNavLink()
    {
        // render the Component:
        var cut = Render(@<EmployeeCard Employee="_employee" />);

        // find an element by ID and test that its markup matches
        // note that the attributes listed (href, id, class) do not have to be in the same order as in the code:
        cut.Find("#detailnavlink").MarkupMatches(
            @"<a href=""employeeedit/1"" id=""detailnavlink"" class=""btn btn-outline-primary btn-sm mb-1"">Edit employee</a>");
    }
}

writing advanced unit tests

testing an injected service

TestProject/InboxWidgetTests.razor

@using BethanysPieShopHRM.App.Components.Widgets
@using BethanysPieShopHRM.App

@inherits TestContext

@code
{
    public InboxWidgetTests() 
    {
        // bUnit exposes the services collection on the TestContext, so services can be injected into the test:
        this.Services.AddScoped<ApplicationState>();
    }

    [Fact]
    public void RenderInboxWidgetWIthValueGreaterThanZero()
    {
        // access the ApplicationState service:
        var applicationState = this.Services.GetService<ApplicationState>();
        applicationState.NumberOfMessages = 5;

        var cut = Render(@<InboxWidget />);
        cut.MarkupMatches("<h3>Inbox</h3><h4>You currently have 5 questions from employees!</h4>");
    }
}