ADR-009 — Testing Strategy

Status

Draft

Context

Coveris has two distinct halves: Django owns all business logic, Angular is a thin signal-based client. A unified testing policy is needed to define what gets tested, where, and by whom — preventing redundancy and ensuring every behavior has exactly one owner.

Decision

Philosophy. Django is the brain. Angular is the screen. If the brain fails, the screen is irrelevant.

Backend: Exhaustive. Every endpoint has a contract test. Every domain rule has a model test. Every bug leaves a regression guard.
Frontend: Test signal integration and enforce structural rules. Do not test DOM depth or PrimeNG rendering.
Contract tests: Every API.md endpoint has a test verifying status codes and response field shapes. A verifier (test_contract_coverage.py) fails if any endpoint lacks one ([[adr-005-a-contract-testing-pipeline|ADR-005-a]]).

Five Test Layers.

Layer	Stack	Owns
Domain / Model	Backend	FSM, computations, constraints, rules engine
Component / Service	Frontend	Signal graph, HTTP integration, guards, interceptors
Contract	Backend	API.md compliance: status codes + response shapes
Architectural guards	Both	Forbidden imports, forbidden patterns, route naming, API.md completeness
Regression guards	Both	Prevent recurrence of specific bugs

Anti-Redundancy Rule. A behavior is tested in exactly one layer. The backend contract test owns “the endpoint returns employee_number as a string”; the frontend service test owns “the service maps it to the component signal”. Neither re-tests the other’s concern.

Test the boundary you own.

Regression Guards. Every bug fixed must leave a preventing test (red → green → permanent). Each has a traceability comment:

# REG: Backlog #42 — employee filter by status returned all statuses

Location: cross-cutting → tests/test_regression_backlog.py; app-specific → apps/<app>/tests/test_regressions.py.

What We Do Not Test.

Excluded	Reason
Framework internals (SimpleJWT, Django ORM, CORS, PrimeNG, Angular CD)	Tested by framework. Sub-ADRs document exceptions.
Snapshot tests	Fragile, high maintenance, low value
Coverage percentage as KPI	Good tests > a number

Sub-decisions

[[adr-009-a-frontend-testing-strategy|ADR-009-a]] — Frontend testing: three layers, signal testing rules, design system enforcement, mock discipline.
[[adr-009-b-backend-testing-strategy|ADR-009-b]] — Backend testing: three layers, contract test rules, fixture topology, markers, security audit exceptions.
[[adr-009-c-ci-integration|ADR-009-c]] — CI integration (deferred).
[[adr-009-d-bdd-e2e-testing|ADR-009-d]] — BDD + E2E with Gherkin + Playwright (deferred).

Operational details (code examples, run commands, rollout plans, gap lists) live in [[testing|docs/dev/testing.md]].

Consequences

(+) Each behavior has exactly one test in exactly one layer.
(+) Regression guards grow the safety net with every bug.
(+) Contract tests keep API.md honest — drift is caught automatically.
(-) Five layers require understanding where each test belongs.
(-) Contract tests for 58 endpoints is a significant upfront investment.