Testing Strategy
Overview
Testing strategy is the plan for what to test at each level and why.
Why It Matters
A good strategy prevents duplicate tests, missing coverage, and wasted maintenance effort.
Core Concepts
- Unit tests cover logic.
- Integration tests cover boundaries.
- E2E tests cover critical journeys.
Mental Models
Use the cheapest test that gives the confidence you need.
Best Practices
- Test the riskier paths more deeply.
- Prefer behavior coverage over implementation coverage.
- Use each test layer for what it does best.
Common Mistakes
- Overloading one test layer to do everything.
- Writing brittle tests for low-value behavior.
- Skipping regression tests after bugs.
Trade-offs
More tests improve confidence, but too many overlapping tests slow down development and maintenance.
Decision Framework
flowchart TD
A[What changed?] --> B{Logic only?}
B -->|Yes| C[Unit test]
B -->|No| D{Boundary involved?}
D -->|Yes| E[Integration test]
D -->|No| F{Critical user flow?}
F -->|Yes| G[E2E test]Examples
- Unit test for data mapping.
- Integration test for API + UI flow.
- E2E test for sign-in.
Checklists
- Did I choose the right test level?
- Is the risk covered?
- Are tests keeping the suite fast enough?
Senior Engineer Notes
Senior engineers design tests as a portfolio, not as a pile. Each layer should earn its place.