How would you structure unit tests for an ASP.NET Web API controller?

Question

ICSM Computer · Answer

To structure unit tests for an ASP.NET Web API controller, you should
isolate the controller logic and mock dependencies. Here’s a clean and testable approach:
1. Structure Your Project
Organize your solution like this:
MyApp/
│
├── MyApp.Api/               → ASP.NET Web API project
│   └── Controllers/
│       └── UsersController.cs
│
├── MyApp.Tests/             → Test project (use xUnit, NUnit, or MSTest)
    └── Controllers/
        └── UsersControllerTests.cs
2. Ensure Controller Follows SOLID
Controllers should:
Use Dependency Injection (DI) for services.Have thin logic: delegate to service layers.Return standard types: IHttpActionResult, ActionResultandlt;Tandgt;, etc.
Example Controller (simplified):
public class UsersController : ApiController
{
    private readonly IUserService _service;
    public UsersController(IUserService service)
    {
        _service = service;
    }
    [HttpGet]
    public IHttpActionResult GetUser(int id)
    {
        var user = _service.GetUser(id);
        if (user == null)
            return NotFound();
        return Ok(user);
    }
}
3. Setup Unit Test Project
a. Install Test Tools:
In MyApp.Tests.csproj:
dotnet add package xunit
dotnet add package Moq
dotnet add package Microsoft.AspNet.WebApi
b. Create Unit Test:
public class UsersControllerTests
{
    private readonly Mockandlt;IUserServiceandgt; _mockService;
    private readonly UsersController _controller;
    public UsersControllerTests()
    {
        _mockService = new Mockandlt;IUserServiceandgt;();
        _controller = new UsersController(_mockService.Object);
    }
    [Fact]
    public void GetUser_ReturnsOk_WhenUserExists()
    {
        // Arrange
        var user = new UserDto { Id = 1, Name = "Anna" };
        _mockService.Setup(s =andgt; s.GetUser(1)).Returns(user);
        // Act
        var result = _controller.GetUser(1) as OkNegotiatedContentResultandlt;UserDtoandgt;;
        // Assert
        Assert.NotNull(result);
        Assert.Equal(1, result.Content.Id);
    }
    [Fact]
    public void GetUser_ReturnsNotFound_WhenUserDoesNotExist()
    {
        // Arrange
        _mockService.Setup(s =andgt; s.GetUser(1)).Returns((UserDto)null);
        // Act
        var result = _controller.GetUser(1);
        // Assert
        Assert.IsTypeandlt;NotFoundResultandgt;(result);
    }
}
4. Best Practices
Mock all external dependencies (DB, APIs, services).Test only controller logic, not the service or DB.Use [Theory] in xUnit for parameterized testing.Test happy and unhappy paths: success, null, exception, bad input.Ensure your controller method returns expected IHttpActionResult.
5. Common Tools
xUnit / NUnit / MSTest – test frameworkMoq – mocking dependenciesFluentAssertions (optional) – more readable assertionsAutoFixture – for auto-generating test data (optional)

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How would you structure unit tests for an ASP.NET Web API controller?

ICSM Computer

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1 Answers

1. Structure Your Project

2. Ensure Controller Follows SOLID

3. Setup Unit Test Project

a. Install Test Tools:

b. Create Unit Test:

4. Best Practices

5. Common Tools

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