Test design interview questions
// 38 QUESTIONS · UPDATED MAY 2026
Test design interview questions covering equivalence partitioning, boundary value analysis, decision tables, state transition, and pairwise testing.
Showing 38 of 38 questions
- What is equivalence partitioning?Junior
A test design technique that groups inputs into classes which are expected to behave the same, then picks one representative from each cl…
- Walk me through using a decision table for a real feature.Mid
List the inputs (conditions), enumerate every combination, and write the expected outcome for each row. Decision tables shine for busines…
- Explain boundary value analysis with a simple example.Junior
Boundary value analysis tests at the edges of equivalence classes — values just below, exactly at, and just above the boundaries. It catc…
- What is a decision table and when would you use one?Junior
A decision table is a grid of input combinations and their expected outputs. Use one when a feature's behaviour depends on multiple input…
- What is state transition testing?Junior
State transition testing models a feature as a finite-state machine — states the system can be in and the events that move it between the…
- What is pairwise testing and why is it useful?Junior
Pairwise testing covers every pair of input combinations rather than every full combination. For systems with many inputs, it shrinks the…
- What is the difference between positive and negative testing?Junior
Positive testing verifies the system works as expected with valid inputs and intended use. Negative testing verifies it handles invalid i…
- Walk through equivalence partitioning for an age field that accepts 18-65.Mid
Partition into Below valid (<18), Valid (18-65), Above valid (>65), plus invalid input classes (non-numeric, negative, missing, decimal).…
- Design test cases for a multi-step wizard using state transition testing.Mid
Model each wizard step as a state, transitions between them as user actions ('next', 'back', 'save and exit'), and design tests that cove…
- When would you choose pairwise over full combinatorial testing? Show a worked example.Mid
Use pairwise when full combinatorial is impractically large and the risk profile suggests bugs are 2-way (most are). Stick with full comb…
- How do you test a function with several boolean inputs?Mid
For ≤ 4 booleans (16 combinations), test all combinations. For 5+, use pairwise to cover every pair, augment with property-based tests fo…
- Compare error guessing with experience-based testing.Mid
Error guessing is a focused technique — the tester guesses likely failure points based on intuition or prior bugs and tests them specific…
- How do you derive test cases from a use case diagram?Mid
For each use case, identify the actors, main success scenario, alternative flows, and exception flows. Each flow becomes one or more test…
- What is cause-effect graphing and when is it more useful than a decision table?Mid
Cause-effect graphing models inputs (causes) and outputs (effects) plus the logical relationships between them as a graph. It's most usef…
- How do you design tests for a feature flag system?Mid
Test the flag's two states (on/off), all combinations with other flags it interacts with, the rollout mechanism (percentage, user targeti…
- Walk through testing a search filter with date ranges, dropdowns, and free text.Mid
Treat each filter as a separate input dimension, apply EP/BVA per dimension, then use pairwise to cover combinations. Add scenarios for c…
- How do you derive test cases from acceptance criteria written in BDD/Gherkin?Mid
Each Given-When-Then scenario maps directly to one test case; Given sets up state, When performs the action, Then asserts the outcome. Au…
- How do you choose between black-box techniques when you have limited time?Senior
Match the technique to the input shape. Numeric ranges → BVA + EP. Boolean combinations → decision table or pairwise depending on count.…
- How does test design change for an AI/ML model output vs deterministic code?Senior
Deterministic code: assert exact outputs, use EP/BVA on inputs, branch coverage. ML models: assert *distributions* and *invariants* (outp…
- How do you design tests for race conditions in a concurrent system?Senior
Combine deterministic concurrency tests (run the same scenario many times in a tight loop with controlled timing), property-based fuzzing…
- Explain risk-based prioritisation for choosing which test designs to apply.Senior
Score each area by likelihood of failure × business impact. Apply the most rigorous test design (decision tables, pairwise, combinatorial…
- How would you derive test data for a payment system with strict regulatory requirements?Senior
Use synthetic data only — never real card numbers or PII in non-prod. Use processor-provided test cards (Stripe, Adyen) for happy paths;…
- What is the difference between a test case, a test scenario, and a test script?Junior
A test scenario is a high-level description of what to test (e.g. 'user can log in'). A test case is a specific, structured set of steps,…
- What is statement coverage and how does it relate to test design?Junior
Statement coverage measures the percentage of executable statements exercised by your tests. As a test design concept, it tells you which…
- What is an exploratory test charter and what does one contain?Junior
A charter is a short, focused brief for an exploratory testing session. It defines what to explore, what information to gather, and optio…
- How do you manage combinatorial explosion when a feature has many input combinations?Mid
Use pairwise (all-pairs) testing to reduce the test set to combinations that cover every pair of values at least once. This typically cut…
- How does test design differ for an API endpoint versus a UI form for the same feature?Mid
API tests go directly to the contract — request shapes, status codes, response bodies, error payloads. UI tests add rendering, validation…
- What is orthogonal array testing and when is it more useful than standard pairwise?Mid
Orthogonal array testing uses predefined combinatorial arrays (L4, L8, L9, L16) that guarantee balanced coverage of factor combinations w…
- How do you design tests that remain maintainable as the system evolves?Mid
Design tests against behaviour and outcomes, not implementation details. Use the Page Object (or equivalent) pattern to isolate selectors…
- When should you NOT write a formal test case?Mid
Skip formal test cases for trivial code already covered by the framework or library (framework internals), one-time throwaway scripts, UI…
- How do you design test data for a database-driven feature?Mid
Create test data as close to the test as possible using factory functions or builders, never depend on pre-existing database state, and u…
- How do you approach branch coverage for a complex conditional logic block?Mid
Enumerate every decision point and its outcomes, then design one test case per branch. For an if/else chain with N conditions, you need a…
- When do you choose exploratory testing over scripted test cases, and how do you make the output auditable?Mid
Choose exploratory testing when the risk is poorly understood, the system is new, you are investigating a bug's blast radius, or when scr…
- How do you build a test strategy when there are no written requirements?Senior
Reconstruct intent from available signals — user stories, design mocks, stakeholder conversations, and existing behaviour — then create a…
- How do you design tests for a feature that integrates with a third-party API you cannot control?Senior
Test your side of the integration against a contract or mock. Test the error-handling paths for every failure the third party can return.…
- How do you design for reusability in a test suite that has grown to hundreds of test cases?Senior
Apply layered architecture: a data layer (factories), an action layer (reusable steps for common user actions), and a test layer (tests t…
- How do you incorporate accessibility requirements into your formal test design?Senior
Treat accessibility criteria (WCAG AA) as first-class acceptance criteria. Design tests at three levels: automated axe-core scanning for…
- How do you establish consistent test design practices across a team with varying skill levels?Lead
Define the techniques the team uses (and why), make examples visible through reviewed test cases, run short technique workshops, and buil…