Reference for FluentAssertions - the canonical .NET fluent-assertion library pairable with xUnit / NUnit / MSTest; provides `.Should()` extension API (`.Should().Be()`, `.Should().BeOfType()`, `.Should().Throw()`, `.Should().BeEquivalentTo()` for deep equality, `.Should().Satisfy()` for predicates, `.Should().BeApproximately()` for floats); rich failure messages with object structure visualization. Covers the v8 license change: v8+ is free for open-source and non-commercial use but requires a paid license for commercial use, while v7 remains fully open-source. Use when a .NET test project needs deep object comparison or better failure output than `Assert.X` gives, when assertions must survive a move between xUnit / NUnit / MSTest, or when picking between v7 and v8+ on license grounds.

Configures and runs Spock - Groovy-based JVM testing framework with given/when/then BDD blocks, where: data tables for parametrized tests, built-in mocking via Mock()/Stub()/Spy(), interaction-based testing (verify method calls in declarative DSL), implicit assertions in then: blocks. Use when working with Java/Kotlin codebases that benefit from Groovy DSL expressiveness, or maintaining existing Spock projects.

Pure-reference catalog of the ISO 8601 vs RFC 3339 distinction. Covers the relationship (RFC 3339 is a strict subset of ISO 8601 designed for internet protocols), the syntactic differences (RFC 3339 disallows ISO 8601's '+02' offset short-form requires '+02:00'; RFC 3339 mandates a date-time separator T or space; ISO 8601 allows much more), the canonical date-time string format (YYYY-MM-DDTHH:MM:SS[.fff]±HH:MM or Z), per-language parser behaviour (Python isoformat, Java Instant.parse, JS Date.parse non-spec), and serialisation rules for APIs. Use when choosing a wire format, parsing third-party datetimes, or auditing time-string handling.

Authors Python test fixtures using mimesis - a fast, type-hinted, locale-aware test-data generator with 46 locales - covering Person / Address / Internet / Datetime providers and the Schema/Field pattern for typed-dict generation. Pairs with factory_boy when referential integrity is needed. Use when the project is Python and the team values speed, type hints, or strong locale coverage over Faker's larger ecosystem.

Builds a canary-validation workflow that compares a canary deploy's metrics against the baseline (current main) - picks the metric set (error rate, p50/p95/p99 latency, business KPIs like checkout-completion), defines per-metric thresholds (absolute + relative-to-baseline), runs a statistical-comparison check (effect size + significance) over the canary's observation window, and emits a promote/rollback verdict. Use as the gate between canary deploy and full rollout - the deterministic version of "the on-call eyeballs the dashboard for 30 min.

Wraps the Serverless Framework (serverless.com) test ecosystem: serverless-offline (local HTTP emulator), serverless-jest-plugin / serverless-mocha-plugin (per-runtime test runners), and the `serverless invoke local` CLI for one-off invocations. Use when testing Lambda functions deployed via the Serverless Framework.

Configures and runs Google OSV-Scanner - open-source SCA against the OSV.dev vulnerability database; supports `osv-scanner scan -r ./` recursive scan + per-lockfile scan via `-L package-lock.json`; SBOM input (CycloneDX / SPDX) for non-standard package managers; `--format json|sarif|markdown|vertical|html` output; suppressions via `osv-scanner.toml` config. Use when the team needs OSS-native SCA without commercial-license overhead, or wants a second-opinion DB pair with Snyk's commercial DB.

Configures and runs Semgrep - pattern-based SAST across 30+ languages with the Semgrep Registry rulesets (`p/owasp-top-ten`, `p/default`, `auto`) plus custom YAML rules; integrates `semgrep ci` for PR-blocking gates with `--baseline-commit` diff-aware scanning, per-finding inline `nosemgrep` suppressions, `--exclude` / `--include` path filters, output formats (`--json` / `--sarif` / `--gitlab-sast` / `--junit-xml`), and severity filter (INFO/WARNING/ERROR). Use when the user runs Semgrep, asks about pattern rules, or needs a low-friction SAST gate without semantic-DB setup.

Wraps Adyen test-mode patterns: test-API-key initialization, the canonical Adyen test cards (Visa 4111 1111 1111 1111; 5454 5454 5454 5454 3DS frictionless; 4917 6100 0000 0000 3DS 2 challenge), the per-flow result codes (Authorised / Refused / Pending / RedirectShopper / Error), the HMAC-SHA256 webhook validation, and notifications-vs-API duality (Adyen separates synchronous API calls from asynchronous notifications). Use when testing Adyen-integrated code.

Authors Espresso UI tests for Android - uses `onView(withId(...)).perform(...).check(matches(...))`, leans on Espresso's automatic synchronization (no `Thread.sleep`), wires `IdlingResource` for app-specific async, runs via `./gradlew connectedAndroidTest` and parses the JUnit XML output. Use when an Android app needs UI tests in Google's first-party framework.

Build-an-X workflow for verifying RTL (right-to-left) layouts - runs the test suite under Arabic / Hebrew / Persian / Urdu locales, asserts the `dir="rtl"` attribute is set, verifies layout mirrors correctly (text alignment, icon positions, scrollbar location), uses logical CSS properties (`start`/`end` over `left`/`right`) per W3C guidance, captures per-locale screenshots for visual review. Use when the app supports RTL languages.

Builds a versioned golden-dataset LLM regression suite for tracking quality across model upgrades: structures a versioned JSONL/CSV golden dataset, configures deterministic eval runs (temperature 0, seed), wires assertion layers (exact, semantic similarity, LLM-as-judge, rubric), enforces a pass-rate threshold with diff reporting vs the baseline model, and gates CI on regression. Use when upgrading an LLM provider model and needing a repeatable before/after quality gate, or when a prompt regression suite must track output quality across model versions over time.

Configures KICS (Keeping Infrastructure as Code Secure), Checkmarx's scanner covering Terraform, Kubernetes, Helm, Dockerfile, OpenAPI, Ansible, ARM, CloudFormation, Pulumi, Crossplane - CLI / Docker / GitHub Action / pre-commit, JSON / SARIF / HTML / JUnit output, custom Rego queries. Use for the widest platform breadth, especially OpenAPI / Pulumi / Crossplane; for the broadest built-in checks with Python custom rules use checkov-policy, for Terraform-only scanning use tfsec-policy, and for a consolidated scanner use trivy-config.

Pure-reference catalog of protobuf3 versioning and breaking-change rules: field-number reservation (reserve on delete; 1..536870911; 19000-19999 reserved), wire-safe vs wire-incompatible changes (add/remove safe with reservation; changing a field number always breaks), compatible type conversions (int32/uint32/int64/uint64/bool; sint32/sint64; string/bytes for UTF-8; enum/int), oneof + map constraints, and buf's four breaking categories (FILE/PACKAGE/WIRE_JSON/WIRE) with rule IDs. Use when designing a schema change or picking a buf breaking ruleset. This is the catalog of what is breaking and why, not a scanner; to detect changes in CI use buf-cli-lint-breaking-build, for the gRPC status-code vocabulary use grpc-status-code-mapping-reference, and for cross-service contract testing use protobuf-compat-checking.

Tests a GraphQL Yoga server (the-guild.dev runtime) with `yoga.fetch()` for in-process, no-network request simulation of queries and mutations, `@graphql-tools/executor-http` for subscription and incremental-delivery (streaming) tests, auth-header pass-through, and production-config gates for disabled introspection and persisted operations; also carries the Mercurius (Fastify GraphQL plugin) in-process `app.inject()` testing patterns in references/mercurius.md. Use to test a GraphQL Yoga or Mercurius server, write query, mutation, or subscription tests, or check production plugin config; for other runtimes use apollo-server-tests or hasura-tests instead, not this skill.

Pure-reference catalog of fuzz-corpus management practices. Defines what a corpus is (seed corpus + evolved corpus saved by the fuzzer), corpus directory layout per libFuzzer / AFL++ / Go native / cargo-fuzz / OSS-Fuzz, the canonical crash-artefact naming (crash-{sha1} / leak-{sha1} / timeout-{sha1}), seed corpus construction strategies (sample-from-prod, sample-from-test-fixtures, from-spec-keywords), corpus minimisation, dictionary files, and the OSS-Fuzz integration corpus sync. Use as the corpus-discipline reference when building a fuzz target or maintaining a long-running fuzz campaign.

Provides concrete code-level fixes for each of the eight recurring flake patterns in flake-pattern-reference: replacing fixed sleeps with framework auto-waits, isolating state in beforeEach fixtures, stable role-based locators, mocking network + clock, seeding RNG, closing leaked resources, and the per-worker DB-schema fix for shared parallel state. Use when a flake is already classified by pattern and you need the specific code change to apply; to classify the pattern first use flake-pattern-reference or flake-axis-bisection, and to quarantine the test while the fix is in review use flaky-test-quarantine.

Wraps GrowthBook Node SDK testing patterns: GrowthBookClient initialization with direct payload (initSync; no network), isOn / getFeatureValue / evalFeature, scoped instances (createScopedInstance) for per-request user context, inline experiment (runInlineExperiment) tests, and tracking-callback assertion patterns. Use when writing tests for code using GrowthBook for flags + experiments.