ASP.NET Core Unit Testing in Action with xUnit, MOQ, and FluentAssertions

Unit testing is an important part of modern software development since it ensures that individual components of your codebase work properly in isolation. There are various tools and frameworks available in ASP.NET Core to help with the unit testing process. In this article, we’ll look at unit testing with three popular tools: xUnit, MOQ, and FluentAssertions. In addition, we will walk through a practical scenario to demonstrate the ideas covered.

Configuring Your ASP.NET Core Project

Before you can begin unit testing, you must first create an ASP.NET Core project. Using the CLI, run the following command to create a new project.

After setting up your project, go to the project folder by navigating to it.

Installing the Required Packages

To perform unit testing with xUnit, MOQ, and FluentAssertions, you can install the necessary NuGet packages using the CLI or Visual Studio NuGet Package Manager.

Writing Your First Test

Let’s say you have a simple service class in your ASP.NET Core application that you want to test. Here’s an example of such a class.

Now, you want to write a unit test for the Add method. Create a new folder in your project called Tests to organize your test files. Inside the Tests folder, create a new class called CalculatorServiceTests.

In this test class, we’ve used xUnit’s [Fact] attribute to mark our test method and FluentAssertions to make our assertions more readable. We’ve arranged the necessary objects, performed the action, and asserted the expected outcome.

Mocking Dependencies with MOQ

In real-world applications, your service classes often depend on other components or external services. To isolate the code you’re testing, you can use MOQ to create mock objects for these dependencies.

Let’s assume that your CalculatorService class depends on a Logger service.

To test the Add method without invoking the real logger, you can create a mock ILogger using MOQ in your test.

In this example, we create a mock ILogger using the new Mock<ILogger>() and pass it as a dependency to the CalculatorService. This allows us to test the Add method without invoking the real logger.

Running Unit Tests

To run your unit tests, you can use the dotnet test command from the command line.

This command will discover and execute all the tests in your project, including the ones you’ve written using xUnit.


Unit testing is a crucial aspect of building reliable and maintainable ASP.NET Core applications. The guide explores the use of xUnit, MOQ, and FluentAssertions to perform unit testing. By following these practices and tools, you can ensure that individual components of your codebase function as expected, making it easier to identify and resolve issues early in the development process.

It is important to remember that unit testing is only one part of the testing process. In addition to unit tests, it is recommended to write integration tests and end-to-end tests to cover different aspects of your application’s functionality. Effective testing helps in building robust and high-quality ASP.NET Core applications.

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