Every change in the code is like a new decoration on a Christmas tree: it can make everything more beautiful, or it can bring the whole structure down. That’s why after each update it’s important not only to check new features but also to ensure that the old functionality still works. This is regression testing.
What is Regression Testing?
Regression testing is the process of re-checking already tested parts of the system to ensure that nothing broke after changes.
Example: you fixed one outlet in your house, but after that the lights and Wi-Fi stopped working. That’s regression.
Why is it needed?
Code changes can be tricky. Even a small fix can affect other, seemingly unrelated parts of the system. Regression testing helps to:
- Detect side effects after introducing new functionality
- Ensure that bugs are really fixed
- Protect old functionality from accidental breakage
Regression is pre-release insurance: “did we break anything?”
When to perform regression testing?
- After a bug fix
- After adding a new feature
- After refactoring
- Before every release
- After merging large pull requests
Even if everything is tested manually or through unit tests - regression is needed to confirm the integrity of the whole system.
Full or Partial?
It’s not always necessary to run all tests. Sometimes it’s enough to test only the affected areas.
Full regression
- Used before important releases, in large systems
- Takes longer, but provides confidence
Partial (selective) regression
- Covers only the affected features and related areas
- Faster, but requires analysis
A skilled QA always assesses risks and decides where a full check is needed and where a local one is enough.
How does automation help in regression?
Manual regression is painful. Repeating the same scenarios over and over is inefficient and exhausting. That’s why automation is an indispensable ally here.
A stable set of automated tests:
- Checks functionality within minutes
- Reduces human error
- Allows running tests on every commit if needed
CI/CD + automated tests = instant regression without the pain.
How is regression testing different from others?
| Test type | Purpose |
|-------------|---------|
| Smoke | Check if the system even starts |
| Sanity | Quick check of specific features |
| Regression | Ensure that old functionality hasn’t broken |
Mistakes to avoid
- Ignoring regression: “well, I checked the new feature, it’s fine!”
- Relying only on unit tests: they don’t show the whole picture
- Running 100 tests manually every time: automate or burn out
- Not updating tests after changes: old regression ≠ relevant regression