The primary role of the ViewModel in MVC is to pass data from the controller to the view. It acts as an intermediary between the controller, which retrieves and processes data, and the view, which displays it. This separation helps keep the presentation logic clean and testable.

In a default ASP.NET Core MVC project, you would typically find the _Layout.cshtml file in the Views/Shared folder. This shared layout file is used to define the common structure and elements that are applied to multiple views across the application.

As a beginner, you would likely start with Visual Studio Community Edition for developing ASP.NET Core applications. It provides a comprehensive development environment with a wide range of features and tools tailored for .NET development, making it suitable for beginners.

The Class Library template in ASP.NET Core is intended for creating reusable class libraries. When you want to encapsulate functionality and share it across multiple projects, such as other ASP.NET Core applications, this template is the right choice. It allows you to create libraries that can be easily referenced and reused.

In ASP.NET Core, you can use the {parameter:regex} constraint to specify a regular expression pattern that a route parameter must match for the route to be selected. This is helpful when you need to apply specific validation rules to route parameters.

The LockoutMaxFailedAccessAttempts option in ASP.NET Core Identity determines the number of invalid access attempts allowed before locking out a user account. After exceeding this limit, the user's account will be temporarily locked to prevent unauthorized access.

Short-circuiting a request in ASP.NET Core middleware means halting the request processing at a specific middleware point and preventing it from continuing further down the pipeline. This can be useful for tasks like authentication, where if authentication fails, further processing can be skipped.

The [NotMapped] attribute in Entity Framework Core is used to specify that a property of an entity should not be mapped to a database column. This is useful when you have properties in your entity that are not supposed to be stored in the database.

ASP.NET Core shifts from the traditional web.config to use JSON-based configuration files, typically named appsettings.json. This change provides a more flexible and human-readable way to configure application settings, and it aligns with modern development practices.

Testing a function that calculates the sum of two numbers would typically fall under Unit Testing. Unit tests focus on testing individual components or functions in isolation to ensure they work as expected. In this case, you're testing a specific function, making it a unit test scenario.