Unit testing is an important means to ensure code quality in C# projects and must be implemented. 1. Select the appropriate testing framework: such as xUnit, NUnit or MSTest, and decide based on team habits or project needs; 2. Reasonably organize the test code: Create a test structure according to the main project structure image, and each test method only tests one behavior, keeping it concise and clear; 3. Isolate dependencies using the Mock framework: such as Moq or NSubstitute, simulate external dependencies to ensure test independence; 4. Automatically run tests and integrate CI/CD: configure automatic testing in GitHub Actions and other processes to prevent error merging, and set automatic running during local development.

When writing C# projects, unit testing is not an option, but an important part of ensuring the quality of the code. If you do not introduce unit tests in development, the maintenance cost will become higher and higher as the function iteration is used, and changing to a small place may cause chain problems.

The following parts are the easiest and most noteworthy points in actual operation.

Select the right test framework

The mainstream testing frameworks in the C# ecosystem include xUnit , NUnit and MSTest . All three can be used, and which one to choose depends mainly on team habits or project history.

• xUnit is lightweight, has a clear structure, suitable for new projects
• NUnit has rich features and supports advanced features such as parameterized testing.
• MSTest is officially provided by Microsoft and is well integrated with Visual Studio.

The installation method is usually to add the corresponding package through the NuGet package manager. for example:

• xunit
• xunit.runner.visualstudio

Then create a class library project, reference these packages and start writing.

Test the way the code is organized

Many people don’t know how to organize test projects at the beginning, but in fact, it is recommended to "mirror" the test structure according to the structure of the main project.

For example:
Your main project is MyApp.Services.User , so the corresponding test project can be called MyApp.Tests , and the class inside is UserTests.cs or a more specific method name such as LoginTests.cs .

This way, the paths are clear when searching for tests and can quickly locate the corresponding module problems.

In addition, try to measure only one behavior for each test method. For example:

 [Fact]
public void Login_WithValidCredentials_ReturnsSuccess()
{
    // Arrange
    var authService = new AuthService();

    // Act
    var result = authService.Login("user", "password");

    // Assert
    Assert.True(result.IsSuccess);
}

Keep the test method concise and clear logic, making it convenient for later maintenance.

Isolate dependencies using Mock framework

The core of unit testing is "unit", that is, it does not rely on external services or databases. At this time, the mock tool is needed to simulate the behavior.

Commonly used C# mock frameworks include Moq and NSubstitute . It is recommended that novices start with Moq. It has intuitive syntax and many community resources.

Let's give a simple example: Suppose you have an interface IEmailService , and you want to test whether the call is correct, but you don't want to actually send an email.

 var mockEmailService = new Mock<IEmailService>();
mockEmailService.Setup(x => x.SendEmail(It.IsAny<string>(), It.IsAny<string>())).Returns(true);

var userManager = new UserManager(mockEmailService.Object);
var result = userManager.SendWelcomeEmail("test@example.com");

Assert.True(result);

In this way, even if the dependent service has not been completed, you can verify whether the logic is correct in advance.

Automatically run tests and integrate CI/CD

Just writing tests is not enough. To make it work, the tests must be automatically run. The usual practice is to add test steps to the CI (Continuous Integration) process.

For example, if you use GitHub Actions on GitHub, you can configure the build process in .github/workflows , adding a sentence:

 - run: dotnet test

This way, every time the code is submitted, all tests will be automatically run, and you will be notified once it fails, preventing errors from being merged into the main branch.

During local development, you can also set the tests to be automatically run after saving, such as the VS Code Test Explorer extension, or built-in functions of Rider and Visual Studio.

In general, unit testing is a habit that requires long-term persistence. You may feel troublesome at first, but the more you can feel its value as you go. If you choose the right tool and straighten the structure, it is actually not complicated, but it is easy to be ignored.

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