By Jochen D.
Shipping a web application means shipping it to an audience you do not control: different browsers, different versions, different operating systems, different screen sizes and a long tail of mobile devices. Checking all of that by hand does not scale, and it is the checking nobody wants to do on a Friday afternoon, which is precisely when it gets skipped.
Automated testing is how you get that coverage repeatably. This page covers why teams automate, what Selenium gives you, and where a hosted grid fits.
Why automate at all?
The case for automation is not that machines are better testers than people. It is that they are tireless and consistent, and that regression checking is the part of testing which is neither creative nor interesting but still has to happen on every change.
- Coverage that does not scale by hand. Manually repeating a checkout flow across a dozen browser and device combinations, on every release, is hours of work that a suite does in minutes.
- Catching regressions early. A bug found by a test on a pull request costs far less than the same bug found by a customer.
- Consistency. A script performs the same steps in the same order every time. Manual testers, reasonably, do not.
- Freeing people for the work only people can do. Exploratory testing, usability judgement and asking whether the feature is any good are not things you can automate, and they get squeezed out when everyone is busy re-checking the same forms.
Automation is not free. Tests need writing and maintaining, and a flaky suite that nobody trusts is worse than no suite at all. The honest framing is that automation is an investment that pays back on anything you run repeatedly, and rarely pays back on something you will check once.
Where Selenium fits
Selenium is the long-standing open-source project for driving real browsers programmatically. You write a test once, in the language your team already uses, and Selenium drives Chrome, Firefox, Safari or Edge through the same steps a person would take.
It is not the only option. Playwright and Cypress have taken a lot of ground for new projects, and for mobile apps you would reach for Appium or Maestro instead. Our roundups of JavaScript testing frameworks and Python testing frameworks go through the alternatives.
Running the same test on every browser
Writing the test is the easy half. The awkward half is having somewhere to run it. A Selenium Grid is a set of machines, each offering particular browsers and versions, that your tests connect to instead of running locally.
You can build one yourself: provision virtual machines, install the browser versions you care about, keep them patched, keep the drivers matching the browsers, and add capacity when the suite gets slow. That is a real and ongoing piece of infrastructure work.
The alternative is a hosted grid. TestingBot maintains the browsers, versions and real mobile devices, and your tests point at our hub instead of your own machines. Tests run in parallel rather than one after another, which is usually where the wall-clock savings come from. If you want to size that, the parallel calculator is the quickest way.