Automated Testing Rules

Core Principles

• Tests protect behavior, not coverage.
• Prefer high-signal tests.
• Tests must fail only on real regressions.
• Test observable behavior, never implementation details.

When Tests Are Required

• Mandatory for: new features, bug fixes, behavior refactors, non-trivial logic, critical paths.
• Not required for: trivial getters/setters, wiring, config, generated code.

Strategy & Pyramid

• Default: unit tests
• Use integration tests at system boundaries.
• Use E2E tests only for critical business flows.
• Prefer integration over heavy mocking.

Design Rules

• Tests must be independent, deterministic, fast, readable.
• Structure: Arrange → Act → Assert.
• Avoid multi-purpose tests.

What To Test

• Business logic
• Edge cases
• Failure paths
• Boundaries & invariants

Naming

should_<expected_behavior>_when_<condition>

Assertions

• Assert outputs, state, and side effects.
• Never assert private methods, internal variables, or call order.

Mocking

• Mock only: external services, DB, queues, filesystem, time.
• Never mock: domain logic, value objects, pure functions.
• Prefer fakes/in-memory adapters.

Test Data

• Use builders/factories.
• Keep data minimal and expressive.

Regression & Refactor Safety

• Every bug fix requires a failing regression test.
• Add tests before behavior refactors.

AI Rules

• Never generate shallow coverage tests.
• Avoid snapshot tests unless requested.
• Ask for clarification instead of guessing behavior.