laravel bind interface to implementation? Why composer update

Question

1. The test class is written according to the document configuration, as shown in the figure: 2. An error is reported when running 3. This is how it is called in the controller 4. After running composer update, no error is reported

世界只因有你 · Answer

composer is used to manage the dependent libraries of PHP projects. Before execution, your project only contains your code. You use the laravel framework, but the code of the framework is incomplete, so an error is reported. If you execute composer update, it will be based on The configuration of composer.json updates all dependencies (download the libraries used in the project), and the dependencies are all satisfied, so it is OK.