Blog

Store Playwright Trace Artifacts in CircleCI

Store Playwright trace artifacts in CircleCI only after failed tests, with correct trace settings, artifact paths, parallel-node naming, and retention controls.

Test a Date Picker with Fixed Time in Playwright

Test date pickers with fixed time in Playwright across month ends, time zones, leap days, and booking cutoffs without flaky waits or host-clock dependence.

Test a Rejected Promise Error Code in Jest

Test rejected Promise error codes in Jest with rejects matchers, typed custom errors, exact assertions, and safeguards against false-positive async tests.

Test Browser Back-Button History in Playwright

Test browser back-button history in Playwright with real navigation, URL and UI assertions, history-state checks, bfcache awareness, and deterministic fixtures.

Test Client-Certificate Authentication with Playwright

Test client-certificate authentication with Playwright using real PEM or PFX identities, exact origin matching, negative mTLS cases, and certificate rotation.

Test Clipboard Read and Write Permissions in Playwright

Test clipboard read and write permissions in Playwright with origin-scoped grants, real Clipboard API assertions, denial paths, and cross-browser caveats.

Comparison

Test Data Builder vs Object Mother

Compare Test Data Builder vs Object Mother patterns, see runnable TypeScript examples, and choose maintainable fixtures without hiding behavior or intent.

Test Downloaded File Contents in Cypress

Test Cypress file downloads by verifying the response headers, saved filename, MIME type, and parsed CSV or PDF content with deterministic cleanup.

Test Downloads with Random Filenames Using Playwright saveAs()

Test Playwright downloads with random filenames by capturing the Download object, choosing a stable saveAs path, and validating the actual file safely.

Test HTML5 Drag and Drop with Cypress DataTransfer

Test HTML5 drag and drop with Cypress DataTransfer using realistic event payloads, drop-zone assertions, debugging tactics, and browser-aware edge cases.

Test Infinite Scroll Until the Last Item in Playwright

Test infinite scroll until the last item in Playwright with deterministic stop signals, bounded loops, network checks, and virtualized-list assertions.

Test JSON Schema Structured Outputs with Promptfoo

Test JSON Schema structured outputs with Promptfoo using deterministic is-json assertions, provider schemas, adversarial cases, custom invariants, and CI reports.

Test Kafka Consumer Rebalancing with Testcontainers

Test Kafka consumer rebalancing with Testcontainers and KafkaJS by adding group members, observing assignments, and proving every partition stays owned.

Test MongoDB Transactions with a Testcontainers Replica Set

Test MongoDB transactions with a Testcontainers replica set using Node.js, real commit and rollback assertions, deterministic startup, and clean isolation.

Test Offline Cache Behavior with Playwright

Test offline cache behavior with Playwright across first load, service-worker fallback, queued writes, and reliable reconnection without false positives.

Test RabbitMQ Dead-Letter Queues with Testcontainers

Test RabbitMQ dead-letter queues with Testcontainers by verifying rejection, expiry, routing keys, x-death headers, policies, and deterministic message recovery.

Test Redis Key Expiration with Testcontainers

Test Redis key expiration with Testcontainers using real TTL commands, isolated containers, refresh boundaries, and deterministic eviction assertions.

Comparison

Test Retries vs Job Retries in CI

Compare test retries vs job retries in CI, contain flaky failures, preserve evidence, and choose the cheapest recovery boundary for each fault.

Test S3 Presigned URLs with Testcontainers and LocalStack

Test S3 presigned URLs with Testcontainers and LocalStack across signed PUT and GET flows, payload metadata, tampering, expiration, and endpoint pitfalls.

Test Shadow DOM with Cypress includeShadowDom

Test Shadow DOM with Cypress includeShadowDom using reliable queries, nested web-component examples, scoped configuration, and debugging tactics for open roots.

Test SNS-to-SQS Filter Policies with LocalStack

Test SNS-to-SQS filter policies with LocalStack, prove accepted and rejected message attributes, and catch routing defects before AWS deployment.

Test SQS Visibility Timeouts with LocalStack

Test SQS visibility timeouts with LocalStack using real receive, redelivery, receipt-handle, deletion, extension, zero-timeout, and idempotency scenarios.

Test WebAuthn with a Virtual Authenticator in Playwright

Test WebAuthn with a virtual authenticator in Playwright to automate passkey registration, sign-in, user verification, and negative browser flows.

Reference

Testcontainers Interview Questions for SDETs

Prepare for Testcontainers SDET interviews with scenario-based questions on lifecycle, networking, readiness, reuse, CI, and reliable integration design.

Testing a Passwordless Email Magic-Link Flow

Test passwordless email magic links across delivery, expiry, single use, wrong-browser handling, deep links, enumeration resistance, and safe redirects.

Testing a Resumable File-Upload API

Test a resumable file-upload API for byte offsets, interrupted transfers, retries, ordering, integrity, expiration, and safe recovery behavior.

Testing a Stripe PaymentIntent 3D Secure Flow

Test a Stripe PaymentIntent 3D Secure flow across challenge success, cancellation, decline, redirect return, and webhook-confirmed payment states.

Testing a Token-Bucket API Rate Limiter

Test a token-bucket API rate limiter with deterministic clocks, burst and refill assertions, concurrent requests, retry headers, and distributed-state checks.

Testing Agent Memory for Cross-User Leakage

Test agent memory for cross-user leakage with canary secrets, paired identities, retrieval tracing, cache isolation, concurrency, and deterministic evidence.

Testing Agent Permission-Boundary Violations

Test agent permission-boundary violations by proving unauthorized tools never execute, including indirect prompts, stale grants, and partial-failure paths.

Testing Agent Plan Recovery After a Tool Failure

Test agent plan recovery after tool failure with fault injection, trajectory assertions, bounded replanning, and outcome-based evaluation for AI agents.

Testing Agent Tool Selection with Distractor Tools

Test AI agent tool selection against plausible distractor tools, measure selection and argument errors, and build reproducible adversarial evaluations.

Testing Agent Tool-Call Retry Behavior

Test agent tool-call retry behavior with scripted transient failures, bounded backoff, idempotency checks, trace assertions, and deterministic terminal outcomes.

Testing AI-Agent Infinite-Loop Detection

Test AI-agent infinite-loop detection with step budgets, repeated-action fingerprints, progress signals, adversarial tools, and deterministic regression cases.

Testing an AWS Lambda Dead-Letter Queue Locally

Test an AWS Lambda dead-letter queue locally with LocalStack, real failed asynchronous invocations, SQS assertions, retry-aware polling, and clean isolation.

Migration

Testing an Embedding-Model Migration for Regressions

Test an embedding-model migration with paired recall, ranking overlap, latency, vector validation, shadow indexes, and controlled rollout gates.

Testing an LLM Guardrail’s False-Positive Rate

Test an LLM guardrail’s false-positive rate with safe-request datasets, confidence intervals, slice analysis, threshold tuning, and production feedback.

Performance

Testing an LLM Time-to-First-Token SLA

Test an LLM time-to-first-token SLA with precise streaming boundaries, controlled workloads, percentile gates, concurrency, warmups, and diagnostic telemetry.

Testing API Content Negotiation with the Accept Header

Test API content negotiation with Accept header quality weights, wildcards, media parameters, 406 responses, response Content-Type, and cache safety.

Testing API Rate-Limit Reset Headers

Testing API rate-limit reset headers correctly verifies remaining quotas, reset timing, Retry-After behavior, and safe client recovery from HTTP 429.

Testing Application Behavior During Read-Replica Lag

Test application behavior during read-replica lag with paused PostgreSQL replay, read-after-write routing, stale-state assertions, fallback, and recovery checks.

Testing Autocomplete Keyboard Accessibility

Test autocomplete keyboard accessibility across arrows, Enter, Escape, focus, ARIA state, and screen-reader announcements with resilient automation.

Testing Closed Shadow Roots with Playwright: Practical Workarounds

Testing closed shadow roots with Playwright requires public-behavior tests or controlled instrumentation. Learn workable seams without brittle private selectors.

Testing Context Loss During Multi-Agent Handoffs

Test multi-agent handoff context loss with constraint canaries, evidence lineage, mutation cases, and executable assertions that expose silent delegation gaps.

Testing Cursor-Pagination API Boundaries

Test cursor-pagination API boundaries with stable ordering, opaque cursor validation, empty and terminal pages, mutation checks, and traversal invariants.

Testing Data-Grid Keyboard Navigation Accessibility

Test data-grid keyboard navigation accessibility across arrows, Home, End, paging, selection, editing, focus visibility, and virtualized rows.

Testing Database Deadlock Retry Logic

Test database deadlock retry logic by forcing a real PostgreSQL cycle, checking SQLSTATE 40P01, bounded backoff, transaction replay, and side effects.

Testing Database Unique-Constraint Race Conditions

Test database unique-constraint race conditions with synchronized PostgreSQL inserts, SQLSTATE assertions, rollback checks, and recovery verification.

Testing Deleted-Document Tombstones in RAG

Test deleted-document tombstones in RAG across vector retrieval, caches, citations, races, and reindexing so removed sources cannot resurface.