Writing tests
Automated testing is the important step of coding down the user interactions you need to test manually each time you make changes to the code : replace the human-driven manual process of reviewing and validating every function of your application, which can take hours !!
Tools
Cypress
I started Cypress.io to perform automated testing. It is an easy desktop based software that mimics the browser within a Jquery driven process. You write your tests in jquery.
Selenium
After loosing all codes from an unplanned SSD crash (yes it happens), I was lazy rewriting the whole code of my cypress tests and looked for a way to record browser interactions. Selenium IDE is a nice record based testing tool that also features assert testing on HTML elements that you can either select on the browser to get the CSS locator, or write the CSS locator yourself.
CSS locators are expressions that point to a specific static or dynamic HTML element of your HTML code : you can test an element value or content using CSS selector syntax !!
Testim
The best online service (saas) you can have for free, and easy to setup for beginners : you record your test sequence on the browser and get a visual preview of all steps, with editing possibility for each step.
Laravel dusk
this is for PHP experts : you code your test in PHP within laravel framework