How can I test dependency injection in ASP.NET Core?

How can I test dependency injection in ASP.NET Core?

You can test dependency injection in ASP.NET Core by using the built-in testing framework and mocking libraries like Moq.

Can you show me a simple example of how to set this up?

Sure! First, create a test project and add references to your main project and Moq. Then, you can write a test like this:

public class MyServiceTests
{
    [Fact]
    public void TestMyService()
    {
        // Arrange
        var mockDependency = new Mock<IMyDependency>();
        mockDependency.Setup(m => m.SomeMethod()).Returns(true);
        var service = new MyService(mockDependency.Object);

        // Act
        var result = service.DoSomething();

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

What if I want to test a controller that uses dependency injection?

You can use the same approach! Create a mock for your service and inject it into the controller. Here's an example:

public class MyControllerTests
{
    [Fact]
    public void Get_ReturnsOkResult()
    {
        // Arrange
        var mockService = new Mock<IMyService>();
        mockService.Setup(s => s.GetData()).Returns(new List<string> { "data1", "data2" });
        var controller = new MyController(mockService.Object);

        // Act
        var result = controller.Get();

        // Assert
        var okResult = Assert.IsType<OkObjectResult>(result);
        var returnValue = Assert.IsType<List<string>>(okResult.Value);
        Assert.Equal(2, returnValue.Count);
    }
}