Fundamentals
Testing starts with concepts, not tools. Before you open Selenium or Postman, you must cleanly separate process from product, verification from validation, severity from priority — otherwise you fix the wrong thing and stop at the wrong point. This section gathers the base vocabulary everything else rests on, from test-case selection to how you word a bug report.
The beginner's main traps hide here too. Testing does not prove the absence of bugs — it reduces risk. The error → defect → failure chain runs one way and does not flip. Smoke is a wide, shallow check, not a deep run. Each such trap is named in its layer. The full map is below.
Topic map
- What testing is — why it exists and why the goal is to reduce risk, not prove there are no bugs.
- QA, QC, and testing — process vs product vs technique, and why they are not synonyms.
- Verification and validation — "building the product right" vs "building the right product".
- Error, defect, failure — the cause-and-effect chain from a human mistake to a runtime failure.
- Causes of bugs — why most defects trace to requirements and communication, not typos.
- The seven ISTQB principles — foundational truths: defect clustering, the pesticide paradox, context-dependence.
- Software life-cycle stages — where testing lives in the SDLC and why it spans the whole cycle.
- SDLC and STLC — the nested testing cycle and how it runs in parallel with development.
- Requirement quality — what makes a requirement testable and why an unverifiable one is defective.
- Test levels — unit, integration, system, acceptance and their scope.
- Test types — functional vs non-functional, plus smoke, sanity, and regression.
- Black-, white-, and grey-box — how much you know of the internals as the axis of classification.
- Positive and negative testing — the happy path vs resilience to invalid input.
- Selecting smoke and regression — criticality vs impact analysis when picking cases.
- The bug report — the mandatory fields and why expected-vs-actual is its heart.
- Severity and priority — technical impact vs business urgency and their independence.
- The defect lifecycle — states from New to Closed and the Reopened loop.
- Suspension and exit criteria — a temporary pause vs the final end of a cycle.
Common traps
| Mistake | Consequence |
|---|---|
| Believing testing proves the absence of bugs | False confidence in a release — testing only shows the presence of defects and reduces risk |
| Calling testing a superset of QA | Inverted hierarchy: testing is a technique inside QC, and QC is part of QA |
| Reversing the error → defect → failure chain | Wrong root-cause hunt: the cause is always a human, the effect a runtime failure |
| Equating severity with priority | Wrong fix ordering; a logo typo can be low severity but high priority |
| Confusing smoke (wide, shallow) with regression (deep) | Either a missed breakage or wasted time running full regression for a hotfix |
| Treating testing as a late phase after development | Expensive defects found in production instead of at requirements review |
| Writing a requirement you cannot verify | No test can confirm it is met — the requirement is defective by nature |
Interview relevance
Fundamentals come up in every junior interview because they instantly separate someone who read the theory from someone who confuses the terms. The interviewer checks not memorization but understanding of relationships: what nests inside what, what causes what, what is independent of what.
What they usually check:
- The purpose of testing — reducing risk and informing, not proving the absence of bugs.
- Telling apart the pairs: QA/QC, verification/validation, severity/priority, smoke/regression.
- The direction of the error → defect → failure chain and where testing sits in the SDLC.
- The contents of a bug report and the defect lifecycle from New to Closed.
Typical wrong answer: "testing is clicking through the app at the end to make sure there are no bugs." That packs three errors — testing is not only dynamic and not only at the end, it does not prove the absence of bugs, and clicking is only a small part of it.