test-strategy-designer

name	Test Strategy Designer
description	Use when asked to design a test strategy, choose a test pyramid shape, define coverage targets, or evaluate testing investments across unit / integration / E2E layers.

Test Strategy Designer

When to invoke

• "Design a test strategy for…"
• "How much unit vs integration vs E2E testing?"
• "What coverage target is right?"
• "Audit our test pyramid."

Workflow

1. Inventory the code under test: modules, public APIs, external integrations, critical paths.
2. Classify risk per module (P0 / P1 / P2) based on blast radius if it breaks.
3. Allocate pyramid: aim for 70% unit, 20% integration, 10% E2E as a starting point; justify deviations.
4. Set coverage targets: 80% line coverage baseline, 90% for P0 modules, branch coverage tracked separately.
5. Define the flaky-test budget: max 1% flaky rate; anything above triggers quarantine.
6. Pick tools per layer: unit (Vitest/JUnit/pytest), integration (Testcontainers), E2E (Playwright).
7. Output: a one-page strategy doc with layer targets, tools, coverage thresholds, and quarantine rules.

Heuristics

• If an E2E test can be rewritten as integration + contract test, do it - E2E is expensive and flaky.
• Contract tests beat mocks for anything that crosses a service boundary.
• Mutation testing (Stryker, PIT) is the only honest way to detect phantom tests.

References

• Google Testing Blog - Test Sizes
• ISTQB Foundation Syllabus
• Martin Fowler - Practical Test Pyramid