How can you find if your website is fast enough? You would like to know an answer to this question before angry customers start complaining in social networks, and probably even before your code is deployed to the production environment.
There are two kinds of tests which can be useful: individual web page performance tests and load tests.
Performance of a web page is usually measured in a real web browser. One of the popular tools to automate such tests is WebPageTest. WebPageTest starts a new instance of chosen web browser, for example, Chrome, navigates to specified URL and waits for the page to complete loading. Loading here includes receiving HTTP response, CSS styles, JS scripts, images, fonts and all other stuff on the page, then rendering the page and executing scripts. WebPageTest measures time to render, time to full complete, number of HTTP requests and few other metrics; captures a timeline of loading of different resources and opening/closing HTTP connections. It can also capture video of page loading and a screenshot. Then it starts the process again to measure repeat visit: it is usually faster because some resources are already cached by the browser.