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) |
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