TestBed is a primary testing utility provided by Angular that allows developers to simulate the environment of an Angular application and facilitate unit testing. It is designed to create an Angular testing module, which is essentially a dynamic version of an @NgModule. This testing module is configured using the TestBed.configureTestingModule() method, where you can specify the components, directives, pipes, and services that are to be included in the testing environment.
When you use TestBed, you are essentially creating a test version of your application's module, which can then be used to instantiate components and services in a controlled testing environment. This enables you to test the behavior of your application in isolation, without having to rely on the actual implementation of its dependencies.
The TestBed utility provides several methods for setting up the testing environment and interacting with it. For example, TestBed.createComponent() is used to create an instance of a component, and TestBed.inject() is used to inject services into your tests, allowing you to test their behavior.
