Contrast UI vs backend testing; design UI-change test cases
Part A: Differentiate UI vs. Backend Testing
For a single-page web application backed by a Backend-For-Frontend (BFF) that interacts with an external payment API, explain precisely:
- Testing Responsibilities: What types of tests belong in UI tests (e.g., visual state, accessibility, client-side validation, routing) versus backend tests (e.g., business rules, data integrity, idempotency)?
- Mocking Strategies: Which layers you would mock or stub in unit, component, contract, integration, and end-to-end (E2E) tests. Justify the fidelity of your mocks and specify what you would refuse to mock.
- Test Reliability: How you would prevent flaky tests (addressing network, time, and asynchronous issues) and detect regressions (using test oracles, golden images, and contract tests).
- Security & Idempotency: Where specific security checks (e.g., XSS, CSRF, authorization) should be implemented and how you would enforce idempotency on retries.
- Coverage Measurement: How you would measure test coverage beyond simple code coverage (e.g., requirements coverage, risk coverage, data coverage).
Part B: Design Test Cases for a Specific UI Change
Consider a scenario where the checkout page is enhanced with a new "Promo Code" text field and an "Apply" button. When a user applies a promo code, the UI asynchronously validates the code with the BFF, updates the total displayed, persists the promo code on the order, and emits an analytics event.
Provide a concise but thorough test matrix for this feature, covering the following categories. For each category, specify the appropriate test type (unit, component, contract, integration, E2E), what components or services would be mocked, and the acceptance oracle (what must be asserted).
- Functional & Negative: Test cases for empty input, whitespace, invalid format, expired codes, single-use codes already used, codes incompatible with cart items, maximum applications per order, case sensitivity, leading/trailing spaces, duplicate apply clicks, and removing an applied code.
- Boundary: Test cases for minimum/maximum length, Unicode/RTL input, emoji, extremely long pasted input, SQL/JS injection attempts (ensuring safe handling), 0% and 100% discounts, and rounding rules for fractional cents.
- Accessibility: Test cases for label/aria attributes, focus order, keyboard-only flow, screen-reader announcements on success/error, and contrast of error states.
- Cross-compatibility: Test cases across major browsers, mobile/desktop viewports, various zoom levels, reduced motion settings, high-contrast mode, slow CPU conditions, and low bandwidth scenarios.
- Resilience: Test cases for offline scenarios, timeouts, server 429/5xx errors, retry/backoff mechanisms, idempotent application of codes, stale promo invalidation if the cart changes, and eventual consistency (ensuring the UI reflects the server's truth).
- Backend/Contract: Test cases for exact request/response schema validation, API versioning, specific error codes, currency and locale effects, time-zone cutoffs for expiry, and audit logging.
- Analytics/Experimentation: Test cases for the event name and payload, once-per-apply semantics, A/B flag behavior, and proper handling of Personally Identifiable Information (PII).
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Contrast UI vs backend testing; design UI-change test cases
Part A: Differentiate UI vs. Backend Testing
For a single-page web application backed by a Backend-For-Frontend (BFF) that interacts with an external payment API, explain precisely:
- Testing Responsibilities: What types of tests belong in UI tests (e.g., visual state, accessibility, client-side validation, routing) versus backend tests (e.g., business rules, data integrity, idempotency)?
- Mocking Strategies: Which layers you would mock or stub in unit, component, contract, integration, and end-to-end (E2E) tests. Justify the fidelity of your mocks and specify what you would refuse to mock.
- Test Reliability: How you would prevent flaky tests (addressing network, time, and asynchronous issues) and detect regressions (using test oracles, golden images, and contract tests).
- Security & Idempotency: Where specific security checks (e.g., XSS, CSRF, authorization) should be implemented and how you would enforce idempotency on retries.
- Coverage Measurement: How you would measure test coverage beyond simple code coverage (e.g., requirements coverage, risk coverage, data coverage).
Part B: Design Test Cases for a Specific UI Change
Consider a scenario where the checkout page is enhanced with a new "Promo Code" text field and an "Apply" button. When a user applies a promo code, the UI asynchronously validates the code with the BFF, updates the total displayed, persists the promo code on the order, and emits an analytics event.
Provide a concise but thorough test matrix for this feature, covering the following categories. For each category, specify the appropriate test type (unit, component, contract, integration, E2E), what components or services would be mocked, and the acceptance oracle (what must be asserted).
- Functional & Negative: Test cases for empty input, whitespace, invalid format, expired codes, single-use codes already used, codes incompatible with cart items, maximum applications per order, case sensitivity, leading/trailing spaces, duplicate apply clicks, and removing an applied code.
- Boundary: Test cases for minimum/maximum length, Unicode/RTL input, emoji, extremely long pasted input, SQL/JS injection attempts (ensuring safe handling), 0% and 100% discounts, and rounding rules for fractional cents.
- Accessibility: Test cases for label/aria attributes, focus order, keyboard-only flow, screen-reader announcements on success/error, and contrast of error states.
- Cross-compatibility: Test cases across major browsers, mobile/desktop viewports, various zoom levels, reduced motion settings, high-contrast mode, slow CPU conditions, and low bandwidth scenarios.
- Resilience: Test cases for offline scenarios, timeouts, server 429/5xx errors, retry/backoff mechanisms, idempotent application of codes, stale promo invalidation if the cart changes, and eventual consistency (ensuring the UI reflects the server's truth).
- Backend/Contract: Test cases for exact request/response schema validation, API versioning, specific error codes, currency and locale effects, time-zone cutoffs for expiry, and audit logging.
- Analytics/Experimentation: Test cases for the event name and payload, once-per-apply semantics, A/B flag behavior, and proper handling of Personally Identifiable Information (PII).