QALingo — ISTQB Foundation

Ready to open your first case, Watson? Let's start with the basics — what testing actually is and why it matters.

What Is Testing?

Chapter 1 · Lesson 1 of 8 · ~5 min

Testing is the process of evaluating a software product to detect differences between expected and actual results, and to assess whether the product meets specified requirements.

Testing serves multiple purposes:

01

Finding defects before they reach users

02

Building confidence that software works as expected

03

Providing information to stakeholders for decisions

04

Preventing defects through early review and feedback

Multiple Choice

Which best describes the primary purpose of software testing?

Now for the 7 Testing Principles — the rules every ISTQB detective lives by. These show up heavily on the exam.

The 7 Testing Principles

Chapter 1 · Core Theory

P1

Testing shows presence of defects, not their absence

You can prove bugs exist. You can't prove they don't.

P2

Exhaustive testing is impossible

You can't test everything. Prioritize by risk.

P3

Early testing saves time and money

A bug in requirements costs 10x less than one in production.

P4

Defects cluster together

80% of bugs live in 20% of the code.

P5

Tests wear out (Pesticide Paradox)

Same tests, repeated = fewer new bugs found.

P6

Testing is context-dependent

Banking app ≠ mobile game. Adapt your approach.

P7

Absence of errors fallacy

Bug-free ≠ useful. Users might still hate it.

Multiple Choice · Principles

A team has run the same regression tests for 8 months. No new defects found in 3 sprints. According to ISTQB, what's the most likely explanation?

Is This a Bug? 🐛

A form accepts negative values for "number of items." A user enters -5 and gets a refund instead of being charged.

Scenario: The developer never added input validation for this field. The code processes any number entered — including negatives — as a valid order quantity.

Every bug has an origin story. Error → Defect → Failure — learn this chain cold. It appears on every ISTQB exam.

Error, Defect & Failure

Chapter 1 · Key Terminology

ERR

Error — a human mistake

e.g. Developer misreads a requirement

DEF

Defect — the imperfection introduced

e.g. Wrong formula written in the code

FAIL

Failure — visible malfunction at runtime

e.g. Users see incorrect totals at checkout

⚠️ Important: Not every defect causes a failure. Some lie dormant and only trigger under specific conditions.

Fill in the Blank

Complete the ISTQB definition:

"Testing can show the ____ of defects, but cannot prove their ____."

Multiple Choice · QA vs QC

A company implements mandatory code reviews to prevent bugs from being introduced. This is an example of:

Multiple Choice · Final Question

Reviewing a requirements document for ambiguities before any code is written is an example of: