thedixitjain Test Organization Conventions
Core Principle
Test directory structure encodes architectural boundaries. If a developer cannot infer the architecture from the test tree alone, the organization is wrong.
Architecture-to-Organization Decision Tree
What is the project's architectural style?
|
+-- Hexagonal / Clean Architecture
| --> Test-type-first: tests/{unit,integration,acceptance,e2e}/
| --> Domain concepts nested within each type
| --> Port contract tests in tests/integration/
|
+-- Vertical Slice
| --> Co-located: features/{slice}/tests/
| --> Cross-slice tests in top-level tests/cross_feature/
|
+-- Modular Monolith
| --> Module-first: tests/modules/{module}/{unit,integration}/
| --> Architecture tests per module (dependency rule enforcement)
| --> Inter-module tests in tests/inter_module/
|
+-- Microservices
| --> Per-service test tree: {service}/tests/{unit,integration,component,contract}/
| --> Contract tests: consumer writes in own repo, provider verifies in own repo
| --> Cross-service E2E in separate project: e2e-tests/
|
+-- Event-Driven
| --> Test-type-first with event-specific categories
| --> Unique: schema contract tests, idempotency tests, saga compensation tests
|
+-- CQRS
| --> Command/Query split within each test type
| --> Unique: projection tests (rebuild + idempotency)
|
+-- Layered (N-Tier)
| --> Mirror source: tests mirror src layer hierarchy
| --> Integration tests verify layer boundary contracts
|
+-- DDD (Tactical)
| --> Bounded-context-first: tests/{context}/domain/aggregates/
| --> Cross-context contract tests in tests/bounded_context_integration/
Comparative Summary
| Architecture | Primary Axis | Secondary Axis | Unique Test Types | Co-located? |
|---|---|---|---|---|
| Hexagonal | Test type | Domain concept | Port contract | No |
| Clean | Test type | Architecture ring | Gateway | No |
| Layered | Mirror source | Test type | Layer boundary | No (Java: yes) |
| Vertical Slice | Feature | Test type | Cross-slice | Yes |
| Modular Monolith | Module | Test type | Architecture, inter-module | No |
| Microservices | Per-service | Test type | Contract (Pact) | No |
| Event-Driven | Test type | Event flow role | Schema, idempotency, saga | No |
| CQRS | Command/Query | Test type | Projection | No |
| DDD | Bounded context | Building block | Aggregate, cross-context | No |
Mirror vs. Feature vs. Hybrid
| Strategy | Best For | Strengths | Weaknesses |
|---|---|---|---|
| Mirror source | Layered, Clean, Hexagonal | Predictable paths, IDE navigation, package-private access (Java) | Feature changes touch multiple dirs |
| Feature co-located | Vertical Slice, React | All feature code in one place, team ownership | Cross-feature tests homeless, hard to run by tier |
| Hybrid (recommended) | Most projects | Type-first for CI stages, feature-nested within | Slightly deeper nesting |
Hybrid pattern (type-first, then feature within):
tests/
unit/
features/
order/test_create_order.py
payment/test_process_payment.py
integration/
features/
order/test_order_repository.py
e2e/
test_checkout_flow.py
Language-Specific Conventions
| Language | File Convention | Discovery Rule | Co-located? |
|---|---|---|---|
| Python (pytest) | test_*.py or *_test.py |
Prefix/suffix match | Separate tests/ (recommended) or inlined |
| TypeScript/JS (Jest) | *.test.ts, *.spec.ts, __tests__/*.ts |
testMatch pattern | Either |
| Java (JUnit/Maven) | *Test.java in mirrored package |
src/test/java mirrors src/main/java |
Mirrored packages |
| Go | *_test.go in same directory |
Language-enforced co-location | Always co-located |
| C# (xUnit/NUnit) | *Tests.cs in parallel project |
Separate test project | Separate project |
| Rust | #[cfg(test)] mod tests inline + tests/ |
Inline for unit, tests/ for integration |
Unit: inline, Integration: separate |
Python conftest.py Placement
Place conftest.py at the lowest directory where fixtures apply. Pytest discovers from outermost to innermost, enabling hierarchical fixture scoping:
tests/
conftest.py # Session fixtures: DB engine, app instance
unit/
conftest.py # Unit-specific: auto-mock markers
integration/
conftest.py # Integration: real DB fixtures
acceptance/
conftest.py # Acceptance: feature file paths
BDD Feature Files
tests/
features/ # Gherkin .feature files by domain
order/
place_order.feature
payment/
process_payment.feature
step_defs/ # Step implementations by domain concept
conftest.py
order_steps.py
payment_steps.py
Organize step definitions by domain concept, not by feature file. Shared steps across features prevent duplication.
Hexagonal Architecture Test Tiers
| Tier | Location | Tests | Adapters |
|---|---|---|---|
| Unit | tests/unit/ | Domain model, value objects, service layer | None (pure) or mock driven ports |
| Integration | tests/integration/ | Individual adapters against real infra | Real infrastructure |
| Acceptance | tests/acceptance/ | Use cases through driving ports | In-memory adapters |
| E2E | tests/e2e/ | Full stack through HTTP/CLI | Real adapters |
Port contract tests: when multiple adapters implement one driven port, create shared contract test suite and run against each adapter.
tests/integration/
test_repository_contract.py # Abstract tests for RepositoryPort
test_postgres_repository.py # Runs contract against Postgres
test_inmemory_repository.py # Runs contract against in-memory
Fixture Organization
| Scope | What | Placement |
|---|---|---|
| Session | Expensive setup (DB engine, app) | Root conftest.py |
| Module | Schema creation, service containers | Directory conftest.py |
| Function | Data cleanup, test isolation | autouse=True in conftest.py |
| Shared across types | Factories, builders | tests/conftest.py or tests/fixtures/ |
Anti-Patterns
| Anti-Pattern | Why It Fails | Fix |
|---|---|---|
| Flat tests/ with no structure | Cannot run by tier, no boundary visibility | Organize by primary axis of architecture |
| Mirroring hex layers in test tree | Couples tests to implementation structure | Organize by test type, not source structure |
| Acceptance tests alongside E2E | Acceptance should use in-memory adapters and run fast | Separate: acceptance/ (fast) vs e2e/ (slow) |
| Feature-coupled step definitions | Steps for login.feature only usable there | Organize steps by domain concept |
| Mixing test tiers in one directory | Cannot run unit-only in pre-commit | Separate directories per tier |
| Cross-module imports in tests | Violates module boundaries | Use inter-module tests with event bus |
| E2E inside single microservice | They span services by definition | Move to separate e2e-tests/ project |
| No contract tests between services | Mocks drift from reality | Consumer-driven contract tests (Pact) |
Source: nWave-ai/nWave → nWave/skills/nw-test-organization-conventions/SKILL.md
Also appears in: nWave-ai/nWave/plugins/nw/skills/nw-test-organization-conventions/SKILL.md