Unlock the Power of Blazor: A Comprehensive Guide to Testing
Blazor, the innovative framework from Microsoft, allows developers to extend their C# development capabilities into browsers, eliminating the need for conventional JavaScript frameworks like React, Vue.js, and Angular. While setting up tests in traditional JavaScript frameworks is relatively straightforward, Blazor requires a more nuanced approach. In this article, we’ll explore how to set up tests for a simple Blazor counter application and cover everything a C# developer might want to test in a Blazor app.
Setting Up a Test Environment
To begin, let’s create a demo project in Visual Studio. Select “New” from the “File” menu, then choose “App” under “Web and Console” and select “Blazor Server App.” On the next page, opt for “No Authentication” and set up your project name and solution name. Click “Create” to complete the process.
Next, we’ll set up a test project. From the “File” menu, select “New Solution” and choose “Tests” under “Web and Console.” Select “xUnit Test Project” and follow the prompts to complete the setup.
Linking the Main Project to the Test Project
To enable the test project to reference and use the main project, we need to create a link inside the test project. Right-click on the test solution in the left sidebar, select “Edit Project File,” and add the following line inside the same group with the SDK version: <ProjectReference Include="../path/to/main-project/main-project.csproj" />.
Setting Up Test Dependencies
Now, let’s install the necessary dependencies. We’ll need bUnit, xUnit, and Moq. Install bUnit by searching for it in the NuGet package manager and selecting both solutions. Repeat this process for xUnit and Moq.
Testing with bUnit
bUnit provides an interface to interact with Blazor components, allowing us to trigger events, find elements, and make assertions. To test a Blazor app with bUnit, we need to create a test suite with a test case function in a class inside the test project. The code inside the test case should follow the Arrange-Act-Assert pattern.
Passing Parameters to Components
Sometimes, components require parameters to render correctly. bUnit provides an interface to work with parameters. We can modify the counter component to accept a DefaultCount parameter and use it to update the component’s currentValue property.
Passing Inputs and Services to Components
Components may rely on external services or fields to function correctly. We can achieve this with bUnit using the Services.AddSingleton method in a test context.
Events
We can trigger an event on an element inside a component using the Find interface of a test context component. This returns an element reference, which has APIs like the Click() method.
Waiting for Async State Update
Some components require time to render the correct data. We can wait for asynchronous state updates using the component.waitForState(fn, duration) method.
Verifying Markups
We can verify if the markup for a component follows a specific pattern using the MarkupMatches bUnit interface method.
Mocking IJSRuntime
IJSRuntime is an interface that enables interaction with JavaScript from.NET code. We can mock the getPageTitle function call to return a specified result.
Mocking HttpClient
Some applications rely on data from a remote server to function correctly. We can eliminate this dependency by mocking HttpClient using a third-party library like RichardSzalay.MockHttp.
By following these steps, you’ll be well on your way to unlocking the full potential of Blazor testing. Remember to explore the advanced uses of bUnit and xUnit to take your testing capabilities to the next level.