As a rule-of-thumb wp-browser should be installed in the root folder of your project.
If your project is a plugin then it should be installed in the root folder of your plugin; if your project is a theme it should be installed in the root folder of your theme.
If your project is a site I'd, personally install it in the site root folder.
The purpose of installing wp-browser in the root folder of a project is to keep the code and its tests under version control together.
Exceptions apply but, for most projects, that's what I would do.
Since Composer is a requirement of wp-browser and the only way to install it you should, first thing, initialize the Composer project.
If you've already initialized the Composer project you can skip this section.
Once you've decided where to install wp-browser navigate to that folder using the terminal and type:
Composer will take you through a number of questions to setup some meta information about your project.
Do not install any dependency yet when asked (unless you know what you're doing) and, as a suggestion, set
wordpress-plugin as "Package Type".
Also, since WordPress is licensed under the GPL-2.0+ you might want to set the "License" of your project to
Once you've initialized the Composer project it's time to
require wp-browser ; you can read more about the usage of the
require command on the Composer documentation.
wp-browser is a testing tool and, as such, should be installed as a project development dependency, not as a normal (production) one.
From the terminal type:
composer require --dev lucatume/wp-browser
This will install the latest stable version of wp-browser and, along with it, Codeception and PHPUnit in the
vendor folder of your project.
Once that's done it's time to move to the setup and configuration of wp-browser.