diff --git a/apps/backend/tests/api/test_health.py b/apps/backend/tests/api/test_health.py
index f0d647f..a7a61b6 100644
--- a/apps/backend/tests/api/test_health.py
+++ b/apps/backend/tests/api/test_health.py
@@ -1,12 +1,9 @@
-from collections.abc import AsyncIterator
+from collections.abc import Callable
 
 import pytest
-from fastapi import FastAPI
 from httpx import AsyncClient
 from sqlalchemy.exc import OperationalError
 
-from app.db.session import get_session
-
 
 async def test_liveness_exposes_service_metadata(client: AsyncClient) -> None:
     response = await client.get("/api/v1/health/live")
@@ -20,15 +17,10 @@ async def test_liveness_exposes_service_metadata(client: AsyncClient) -> None:
     }
 
 
-async def test_readiness_reports_the_timescaledb_version(app: FastAPI, client: AsyncClient) -> None:
-    class ReadySession:
-        async def scalar(self, *_: object, **__: object) -> str:
-            return "2.22.1"
-
-    async def override() -> AsyncIterator[ReadySession]:
-        yield ReadySession()
-
-    app.dependency_overrides[get_session] = override
+async def test_readiness_reports_the_timescaledb_version(
+    fake_session: Callable[..., None], client: AsyncClient
+) -> None:
+    fake_session(result="2.22.1")
 
     response = await client.get("/api/v1/health/ready")
 
@@ -41,16 +33,9 @@ async def test_readiness_reports_the_timescaledb_version(app: FastAPI, client: A
 
 
 async def test_readiness_returns_503_when_the_extension_is_missing(
-    app: FastAPI, client: AsyncClient
+    fake_session: Callable[..., None], client: AsyncClient
 ) -> None:
-    class SessionWithoutExtension:
-        async def scalar(self, *_: object, **__: object) -> None:
-            return None
-
-    async def override() -> AsyncIterator[SessionWithoutExtension]:
-        yield SessionWithoutExtension()
-
-    app.dependency_overrides[get_session] = override
+    fake_session(result=None)
 
     response = await client.get("/api/v1/health/ready")
 
@@ -67,16 +52,9 @@ async def test_readiness_returns_503_when_the_extension_is_missing(
     ids=["erreur_sqlalchemy", "erreur_reseau_asyncpg"],
 )
 async def test_readiness_returns_503_when_database_is_unreachable(
-    app: FastAPI, client: AsyncClient, failure: Exception
+    fake_session: Callable[..., None], client: AsyncClient, failure: Exception
 ) -> None:
-    class UnreachableSession:
-        async def scalar(self, *_: object, **__: object) -> None:
-            raise failure
-
-    async def override() -> AsyncIterator[UnreachableSession]:
-        yield UnreachableSession()
-
-    app.dependency_overrides[get_session] = override
+    fake_session(failure=failure)
 
     response = await client.get("/api/v1/health/ready")
 
diff --git a/apps/backend/tests/conftest.py b/apps/backend/tests/conftest.py
index e855f1b..950fc69 100644
--- a/apps/backend/tests/conftest.py
+++ b/apps/backend/tests/conftest.py
@@ -1,13 +1,14 @@
 import os
-from collections.abc import AsyncIterator, Iterator
+from collections.abc import AsyncIterator, Callable, Iterator
 
 import pytest
 from fastapi import FastAPI
 from httpx import ASGITransport, AsyncClient
 
 from app.core.config import get_settings
-from app.db.session import get_engine, get_session_factory
+from app.db.session import get_engine, get_session, get_session_factory
 from app.main import create_app
+from tests.factories import FakeSession
 
 
 # Piege : les variables d'environnement priment sur apps/backend/.env. Celles qu'on ne
@@ -52,3 +53,14 @@ async def client(app: FastAPI) -> AsyncIterator[AsyncClient]:
     transport = ASGITransport(app=app)
     async with AsyncClient(transport=transport, base_url="http://test") as async_client:
         yield async_client
+
+
+@pytest.fixture
+def fake_session(app: FastAPI) -> Callable[..., None]:
+    def install(result: object = None, failure: Exception | None = None) -> None:
+        async def override() -> AsyncIterator[FakeSession]:
+            yield FakeSession(result=result, failure=failure)
+
+        app.dependency_overrides[get_session] = override
+
+    return install
diff --git a/apps/backend/tests/factories.py b/apps/backend/tests/factories.py
new file mode 100644
index 0000000..05ba3fc
--- /dev/null
+++ b/apps/backend/tests/factories.py
@@ -0,0 +1,37 @@
+from typing import Any
+
+from app.core.config import Settings
+
+SETTINGS_DE_TEST: dict[str, Any] = {
+    "env": "local",
+    "debug": False,
+    "log_level": "WARNING",
+    "cors_origins": "",
+    "secret_key": "secret-de-test",
+    "database_url": "postgresql+asyncpg://enervision:change_me@localhost:5433/enervision_test",
+}
+
+
+class FakeSession:
+    """Session factice : renvoie `result`, ou leve `failure` si elle est fournie."""
+
+    def __init__(self, result: object = None, failure: Exception | None = None) -> None:
+        self._result = result
+        self._failure = failure
+
+    async def scalar(self, *_: object, **__: object) -> object:
+        return self._repondre()
+
+    async def execute(self, *_: object, **__: object) -> object:
+        return self._repondre()
+
+    def _repondre(self) -> object:
+        if self._failure is not None:
+            raise self._failure
+        return self._result
+
+
+# Piege : les arguments nommes priment sur l'environnement et sur .env, contrairement
+# aux variables posees par la fixture `environment`, qui restent surchargeables.
+def make_settings(**overrides: Any) -> Settings:
+    return Settings(**{**SETTINGS_DE_TEST, **overrides})