Master Unit Testing in .NET 8 Blazor WebAssembly: xUnit, BUnit & Moq for CRUD Components

Unit Testing Blazor Components with Moq and Bunit

Unit testing in Blazor is essential to ensure that your components behave as expected. This article demonstrates how to effectively test Blazor components using Moq for mocking services and Bunit for rendering and interacting with components in a test environment. We’ll walk through various testing scenarios, including adding, fetching, updating, and deleting products in a Blazor application.

Introduction to Bunit and Moq

Bunit is a testing library designed for Blazor components. It allows you to render components in isolation and perform actions such as interacting with the UI, asserting the output, and verifying the behavior of the components.

Moq is a popular .NET library for mocking dependencies in unit tests. It allows you to simulate the behavior of complex services and verify that your components interact with these services as expected.

Testing Scenarios

Let's explore several common scenarios where Bunit and Moq are used to test Blazor components:

1. Adding a Product

When a user adds a product through the UI, the component needs to capture the input, create a product object, and call the service method to add the product to the database. Testing this flow involves verifying that the component correctly captures user input and calls the service with the correct data.

In the test scenario:

• We mock the product service to ensure it simulates the addition of a product.
• We render the AddProductComponent using Bunit and simulate user interactions like filling in the product details and clicking the "Add Product" button.
• The test verifies that the component correctly invokes the service method with the expected product details.

2. Fetching and Displaying Products

Fetching a list of products from a service and displaying them in a table is a common requirement. Testing this involves ensuring that the component correctly displays the data provided by the service.

In the test scenario:

• A mock service returns a predefined list of products.
• The ProductListComponent is rendered, and we check that the component correctly displays the data in a table.
• The test asserts that the table has the correct number of rows and that each row contains the expected product details.

3. Deleting a Product

Deleting a product involves interacting with the UI to remove an item and verifying that the service is called to delete the product from the backend.

In the test scenario:

• The mock service is configured to return a list of products and simulate the deletion of a product.
• We render the ProductListComponent and simulate clicking the delete button for a product.
• The test verifies that the service's delete method is called with the correct product ID and that the component updates the UI to reflect the deletion.

4. Fetching and Displaying a Single Product

When a component is responsible for fetching and displaying details of a single product, it’s crucial to ensure that it correctly retrieves and displays the data.

In the test scenario:

• A mock service provides the details of a specific product.
• The GetProductByIdComponent is rendered with a predefined product ID.
• The test checks that the product details are correctly displayed in the component.

5. Updating a Product

Updating product information typically involves pre-filling a form with existing data and allowing the user to edit and save changes. The component must correctly load the product data, capture the updated input, and call the service to update the product.

In the test scenario:

• The mock service returns the details of a product and simulates an update operation.
• We render the UpdateProductComponent, ensuring the input fields are correctly pre-filled with the product details.
• The test simulates updating the product’s details and clicking the update button, verifying that the service is called with the updated product information.

Conclusion

Unit testing Blazor components using Moq and Bunit provides a robust way to ensure your components behave correctly. By mocking the service layer and simulating user interactions, you can test the component logic in isolation, leading to more reliable and maintainable Blazor applications. Whether adding, fetching, updating, or deleting products, these tests give you confidence that your components will function correctly in a real-world scenario.