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In this article, let's learn about how to unit test Hosted Services in WebAPI in ASP.NET Core.

Note: If you have not done so already, I recommend you read the article on Perform Background Workloads in Hosted Service using Channels in ASP.NET Web API.

Table of Contents

1. Introduction
2. Why Unit Testing?
3. What is a Hosted Service?
4. Unit Testing Hosted Service
5. Summary

Introduction

In ASP.NET Core, hosted services plays a vital role in simplifying background jobs which needs to run periodically to perform operations. Most common use cases include:

• Processing uploaded excel in background
• Sending emails in background
• Other long running operations, etc

If you are aware of Hosted Service and Unit Testing then you can skip the next two sections and jump to the section on Unit Testing Hosted Service.

Why Unit Testing ?

When writing software, we want to ensure that the code is covered by tests, which verify the required behavior and catch any regressions. Unit testing is a crucial practice in software development as it helps identify issues early in the development process. When it comes to service registration, unit testing offers the following benefits:

• Validation: Unit tests verify that the necessary services are registered correctly, avoiding runtime errors caused by missing or misconfigured dependencies.
• Refactoring: Unit tests provide a safety net when refactoring code by ensuring that service registration remains intact during code changes.
• Documentation: Well-written unit tests serve as living documentation, illustrating how services should be registered and ensuring consistency across the application.

Note: If you have not done so already, I recommend you read the article on Implementing TDD in C# .Net.

What is a Hosted Service ?

Hosted services in ASP.NET Core have been available since version 2.1, and they support performing background tasks outside of the main requests flow. The best way to understand when and where hosted services can be applied is to begin using them. Hosted services are based on the abstract concept of a background service. The terms hosted service and background service are often used interchangeably. I'll refer to them by both names throughout this article. Hosted services are available under Microsoft.Extensions.Hosting namespace.

To know more about Hosted Service or Background Service is outside the scope of this article. I'll write a separate article on Background Services in ASP.NET Core. For now lets understand walkthrough how to use Hosted Service.

Unit Testing Hosted Service

We are going to write unit tests for the Data Migration Hosted Service which we used in our previous article on Perform Background Workloads in Hosted Service using Channels in ASP.NET Web API. Here is the quick reference of the hosted service used in that article.

To unit test the DataMigrationService Hosted Service, follow these steps:

1. Create a new test class, let's call it HostedSrviceTests, and add a test method using the [Fact] attribute.
2. In the test method, instantiate a DataMigrationChannel which we used in previous article and ServiceCollection from the Microsoft.Extensions.DependencyInjection namespace. This collection will act as the container for our services.
3. Use Moq to Mock the IUnitOfWork and add it to the ServiceCollection and call BuildServiceProvider() to build the ServiceProvider instance.
4. Finally let's use NullLogger<DataMigrationService>.Instance from Microsoft.Extensions.Logging.Abstractions namespace instead of Mocking it as we are not going to test the logger. Moreover mocking Logger is a complex step.
5. Next Call the MigrateData method in the DataMigrationChannel object to add message to the channel.
6. Then, instantiate the DataMigrationService class with the above instantiated parameters and call the StartAsync method with default CancellationToken to start the service.
7. Now call ExecuteTask from the DataMigrationService class to execute the task. This will make the ExecuteAsync of actual background service to run.
8. Perform assertions using the IsCompletedSuccessfully result on the ExecuteTask of DataMigrationService. Check for its success.
9. Additionally, verify IUnitOfWork using Moq Verify methods.

By executing above test we can validate background services in ASP.NET Core apps. The same can be used to validate worker services in dotnet.

Summary

Unit testing hosted services in ASP.NET Core is a crucial step to ensure that they are working as expected. By writing unit tests, you can validate behavior, identify issues early on, and maintain a reliable and robust application. The examples and techniques covered in this article provide a solid foundation for performing unit tests on hosted services, promoting software quality and maintainability in ASP.NET Core applications.