Testing Strategies

QuadKit is built for testability. Because services depend on protocols and are wired by the container, you can replace any infrastructure dependency with an in-memory implementation and run your tests entirely in-process. The quadkit-testing package provides the building blocks.

uv add --dev quadkit-testing

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1. Fakes Over Mocks

QuadKit favours fakes — real, in-memory implementations of a protocol — over mocks that merely record calls. Fakes behave like the real thing (you can read back what you wrote), so your tests exercise genuine logic at unit-test speed.

Test type	Dependencies	Speed
Unit	Fakes for everything	Fastest
Integration	Real backends (Postgres, Redis)	Slower
End-to-end	A booted app via a test client	Slowest

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2. Built-in Fakes

quadkit-testing ships fakes for the common contracts:

from quadkit.testing import (
    FakeCache,          # CacheBackendProtocol
    FakeEventBus,       # EventBusProtocol
    FakeClock,          # ClockProtocol (manually advanced)
    FixedClock,         # ClockProtocol (frozen at a fixed time)
    FakeLogger,
    FakeCommandBus,
    FakeQueryBus,
    FakeUnitOfWork,
    FakeMetricsCollector,
)

Use a fake exactly where the real implementation would go — inject it as the protocol:

import pytest
from quadkit.testing import FakeCache
from my_app.services import OrderService


@pytest.mark.asyncio
async def test_order_is_cached():
    cache = FakeCache()
    service = OrderService(cache=cache)

    await service.place_order(order_id="123")

    # FakeCache implements CacheBackendProtocol — read the value straight back
    cached = await cache.get("order:123")
    assert cached.unwrap() is not None

FakeEventBus records the events your code publishes; consult the quadkit-testing package docs for its inspection helpers.

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3. Controlling Time

For expiry, scheduling, or timestamp logic, inject a deterministic clock instead of the system clock:

from datetime import datetime, UTC
from quadkit.testing import FixedClock

clock = FixedClock(datetime(2026, 1, 1, 12, 0, tzinfo=UTC))
service = TokenService(clock=clock)

token = await service.create_token(ttl_seconds=3600)
assert token.expires_at == datetime(2026, 1, 1, 13, 0, tzinfo=UTC)

FakeClock is the manually-advanceable variant when you need to simulate the passage of time within a test.

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4. Overriding Services in the Container

When you boot the real application but want to replace one dependency, use a testing_mode container and override():

from quadkit import Container

container = Container(testing_mode=True)
container.override(UserRepository, FakeUserRepository())

override() is only available when testing_mode=True, so it can never be used by accident in production.

Modules expose stub() for the same purpose at the module level — it returns a test-mode variant backed by in-memory/no-op providers:

from quadkit import Application
from quadkit.web.module import WebModule

async with Application.boot(modules=[WebModule.stub()]) as app:
    ...

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5. Test Clients

quadkit-testing provides per-subsystem test beds and clients that boot the relevant providers in-process:

Client	Bed	For
WebTestClient	WebTestBed	Sending requests to your controllers without a real server
DatabaseTestClient	DatabaseTestBed	Repository tests against a throwaway database
TaskTestClient	TaskTestBed	Enqueue/execute background tasks
AITestClient	AITestBed	Drive AI services with a stubbed LLM

from quadkit.testing import WebTestBed


async def test_get_profile():
    async with WebTestBed(create_app) as bed:
        client = bed.client
        response = await client.get("/api/profile")
        assert response.status_code == 200

See the package docs for each bed’s exact setup options.

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6. Protocol Compliance Suites

A standout feature of quadkit-testing: reusable compliance suites that verify your implementation of a protocol behaves correctly. Run the suite against your backend to guarantee it honours the contract:

from quadkit.testing import CacheBackendCompliance
from my_app.infrastructure.cache import MyCustomCache


class TestMyCacheCompliance(CacheBackendCompliance):
    def make_backend(self):
        return MyCustomCache()

Compliance suites ship for caches, repositories, event buses, queues, vector stores, search engines, audit stores, and more — so custom implementations stay drop-in compatible.

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7. Separating Test Tiers

Mark slower, infrastructure-dependent tests so you can run the fast suite during development:

uv run pytest -m "not integration"

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Next Steps

• quadkit-testing package — full fixture and helper reference
• Dependency Injection — testing_mode and override()
• Result Pattern — asserting on Ok / Err