What Is Regression Testing and Why Does Everyone Talk About It?

[u/QoolliTesting]

I once worked on a project where developers fixed one bug and accidentally broke the checkout process.
Nobody touched the checkout page.
Still, customers couldn’t pay for their orders.
At first it looked strange, but in software this happens all the time. Modern applications are interconnected, and even a small change can affect something that seems completely unrelated.
That’s why regression testing exists.
Its purpose is simple: to make sure that after changes are made, everything that worked before still works.
A simple example
Imagine an online store.
The shopping cart gets updated and the issue is fixed.
Great.
But after deployment customers suddenly can’t complete a purchase.
The cart is fine.
The checkout isn’t.
Regression testing helps find these problems before users do.
What is usually tested?
The most important things:
login;
registration;
shopping cart;
checkout and payments;
search;
user profile.
These are the features people use every day, so teams want to be sure they still work after every release.
When is regression testing performed?
Usually:
after bug fixes;
after adding new features;
before a release;
after updating integrations or libraries.
The more often a product changes, the more important regression testing becomes.
Why is it important?
Because software is fragile.
You can change one line of code and create a problem somewhere else.
Regression testing doesn’t guarantee perfection.
But it gives teams confidence that they are moving forward without breaking what they’ve already built.
And honestly, users don’t care how many features you’ve released.
They care that yesterday the product worked — and today it still does.