Testing Basics

A simple introduction to software testing for beginners.

1. What is software testing?

Software testing is the activity of checking if a software product works the way it should.

When you test, you try to answer questions like:

Does the feature do what the requirements say?
Does it work for different users, devices, and browsers?
What happens when the user does something unexpected?
Are there bugs (defects) that we should fix before release?

Why testing matters:

Bugs found early are cheaper to fix.
Testing protects the users (and the company's reputation).
Testers give the team confidence to release.

💡 Remember: Testing cannot prove the software has zero bugs. Testing shows the software is good enough to use, based on what we checked.

2. Types of testing

2.1 Unit testing

Tests one small piece of code (a function or method) alone.
Usually written and run by developers, not testers.
Very fast, very small.

2.2 Integration testing

Tests if two or more parts work together.
Example: does the login page talk correctly to the database?

2.3 System testing

Tests the whole application as one complete system.
Testers usually do this. It uses real user flows (end-to-end).

2.4 UAT (User Acceptance Testing)

Real users or business people check if the software is ready for them.
Usually the last step before go-live.
Question: "Can the user do their job with this?"

2.5 Regression testing

Re-run old tests after a change, to check that nothing old broke.
Very common task for testers. Often the first thing to be automated.

2.6 Smoke testing

A quick check that the most important features work.
Done on a new build before deeper testing.
Think: "Does the app even start? Can I log in?"

2.7 Sanity testing

A narrow check of one specific area after a small fix.
Example: developer fixed the password reset — you test only password reset.
Smoke = wide and shallow. Sanity = narrow and focused.

2.8 Exploratory testing

Testing without a script — you explore the app, learn it, and try to break it at the same time.
Uses your experience and curiosity.
Great for finding bugs that scripted tests miss.

3. SDLC — Software Development Life Cycle

The SDLC is the life of a software project, from idea to release. Common phases:

Requirements — what should the software do?
Design — how will we build it?
Development — developers write the code.
Testing — we check the software. ← You are here!
Release — the software goes live.
Maintenance — fix bugs, add small changes.

💡 Testers should join early (at the requirements phase), not only after development. Finding a wrong requirement early saves a lot of time.

4. STLC — Software Testing Life Cycle

The STLC is the life of the testing work inside the SDLC:

Requirement analysis — understand what to test.
Test planning — decide scope, time, people, tools.
Test case design — write test cases.
Environment setup — prepare test servers, data, devices.
Test execution — run the tests, log results.
Defect reporting — write bug reports, retest fixes.
Test closure — summarize what was tested, lessons learned.

5. Test levels (from small to big)

Level	What is tested	Who usually does it
Unit	Single function	Developers
Integration	Parts working together	Developers / Testers
System	The whole application	Testers
Acceptance (UAT)	Business needs	Users / Business / Testers

6. Severity vs Priority

These two words are different, and junior testers often mix them up.

Severity = how BAD is the bug (technical impact)

Critical — the app crashes, data is lost, security hole.
Major — an important feature does not work.
Minor — small problem, workaround exists.
Trivial — typo, small UI issue.

Priority = how SOON should we fix it (business decision)

High — fix now, before release.
Medium — fix in the normal queue.
Low — fix when there is time.

Example combinations

Bug	Severity	Priority	Why
App crashes on login	Critical	High	Everyone is blocked
Typo on the home page logo	Trivial	High	Cheap to fix, very visible
Rare crash in an old admin page	Major	Low	Almost nobody uses that page

💡 Testers usually set severity. The product owner or manager usually sets priority. But this can be different in each company — ask your team.

7. Quick self-check

What is the difference between smoke and sanity testing?
Who usually does UAT?
A bug breaks an important feature but on a page nobody uses. Is severity high or low? What about priority?
What are the 7 phases of the STLC?

If you can answer these, you understand the basics. 🎉