One of the best practices in .NET Core and C# is to use inversion of control (IoC) to decouple components and improve testability. IoC is a design pattern that allows you to invert the flow of control in your application. Instead of your code controlling the creation and management of objects, IoC containers take over this responsibility. This means that your code is no longer tightly coupled to specific implementations, making it more modular and easier to test.

IoC containers work by registering dependencies and then injecting them into the classes that require them. This allows you to easily swap out implementations without having to modify the classes that use them. For example, if you have a class that depends on a database connection, you can register the connection with the IoC container and then inject it into the class. If you later decide to switch to a different database, you can simply update the registration and the new connection will be injected into the class.

Using IoC can also improve the testability of your code. By decoupling components, you can easily replace dependencies with mock objects during testing. This allows you to isolate the code you are testing and focus on specific scenarios without having to worry about the behavior of other components. Additionally, IoC containers can help you manage the lifetime of objects, ensuring that they are properly disposed of when they are no longer needed.

// Example of registering a dependency with an IoC container
services.AddScoped<IDatabaseConnection, SqlDatabaseConnection>();

// Example of injecting a dependency into a class constructor
public class MyClass
{
    private readonly IDatabaseConnection _connection;

    public MyClass(IDatabaseConnection connection)
    {
        _connection = connection;
    }

    public void DoSomething()
    {
        // Use the database connection
    }
}