diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..1b865cd
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+
+jobs:
+  backend-tests:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Run backend tests in Docker
+        run: docker compose run --rm --no-deps --build bench-processor python -m pytest -q tests
diff --git a/README.md b/README.md
index fe643d3..047367f 100644
--- a/README.md
+++ b/README.md
@@ -39,4 +39,18 @@ docker compose exec bench-processor python -m alembic -c alembic.ini revision --
 Check alembic/versions newly created migration, then apply migration:
 ```
 docker compose exec bench-processor python -m alembic -c alembic.ini upgrade head
-```
\ No newline at end of file
+```
+
+## Tests
+
+Run backend tests inside the Docker container:
+
+```bash
+docker compose run --rm --no-deps bench-processor python -m pytest -q tests
+```
+
+If you want to run tests against the latest image rebuild:
+
+```bash
+docker compose run --rm --no-deps --build bench-processor python -m pytest -q tests
+```
diff --git a/bench_processor/requirements.txt b/bench_processor/requirements.txt
index 25663d2..586d3cf 100644
--- a/bench_processor/requirements.txt
+++ b/bench_processor/requirements.txt
@@ -2,4 +2,6 @@ fastapi==0.115.0
 uvicorn[standard]==0.30.6
 sqlalchemy==2.0.32
 psycopg[binary]==3.2.2
-alembic==1.13.2
\ No newline at end of file
+alembic==1.13.2
+pytest==8.4.2
+httpx==0.27.2
diff --git a/bench_processor/tests/conftest.py b/bench_processor/tests/conftest.py
new file mode 100644
index 0000000..05d4d09
--- /dev/null
+++ b/bench_processor/tests/conftest.py
@@ -0,0 +1,45 @@
+import sys
+from pathlib import Path
+
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import create_engine
+from sqlalchemy.orm import Session, sessionmaker
+from sqlalchemy.pool import StaticPool
+
+PROJECT_ROOT = Path(__file__).resolve().parents[1]
+if str(PROJECT_ROOT) not in sys.path:
+    sys.path.insert(0, str(PROJECT_ROOT))
+
+from app.db import Base, get_db
+from app.main import app
+
+
+@pytest.fixture(scope="module")
+def test_db_session() -> Session:
+    engine = create_engine(
+        "sqlite+pysqlite:///:memory:",
+        connect_args={"check_same_thread": False},
+        poolclass=StaticPool,
+    )
+    testing_session_local = sessionmaker(bind=engine, autoflush=False, autocommit=False)
+    Base.metadata.create_all(bind=engine)
+
+    db = testing_session_local()
+    try:
+        yield db
+    finally:
+        db.close()
+        Base.metadata.drop_all(bind=engine)
+        engine.dispose()
+
+
+@pytest.fixture(scope="module")
+def client(test_db_session: Session):
+    def override_get_db():
+        yield test_db_session
+
+    app.dependency_overrides[get_db] = override_get_db
+    with TestClient(app) as test_client:
+        yield test_client
+    app.dependency_overrides.clear()
diff --git a/bench_processor/tests/test_health_check.py b/bench_processor/tests/test_health_check.py
new file mode 100644
index 0000000..40823c2
--- /dev/null
+++ b/bench_processor/tests/test_health_check.py
@@ -0,0 +1,5 @@
+def test_health_returns_ok(client) -> None:
+    response = client.get("/api/health")
+
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}
diff --git a/bench_processor/tests/test_log_stool.py b/bench_processor/tests/test_log_stool.py
new file mode 100644
index 0000000..d73e995
--- /dev/null
+++ b/bench_processor/tests/test_log_stool.py
@@ -0,0 +1,40 @@
+import pytest
+from sqlalchemy.orm import Session
+
+from app.db.models import StoolRecord, User
+
+
+@pytest.fixture(scope="module", autouse=True)
+def seed_default_user(test_db_session: Session) -> None:
+    test_db_session.add(User(user_id=1, name="Test User", email="test@example.com"))
+    test_db_session.commit()
+
+
+def test_insert_stool_record_writes_row(client, test_db_session: Session) -> None:
+    payload = {"wetness": 0.67, "experience": 1.0}
+    response = client.post("/api/1/stool", json=payload)
+
+    assert response.status_code == 200
+    assert response.json() == "created"
+
+    rows = test_db_session.query(StoolRecord).all()
+    assert len(rows) == 1
+    assert rows[0].user_id == 1
+    assert rows[0].wetness_rating == 0.67
+    assert rows[0].experience_rating == 1.0
+
+
+def test_insert_stool_record_returns_validation_error_when_user_missing(client) -> None:
+    payload = {"wetness": 0.67, "experience": 1.0}
+    response = client.post("/api/2/stool", json=payload)
+
+    assert response.status_code == 400
+    assert response.json() == {"message": "validation error: user_id 2 not found"}
+
+
+def test_insert_stool_record_rejects_out_of_range_values(client) -> None:
+    payload = {"wetness": 1.2, "experience": -0.1}
+    response = client.post("/api/1/stool", json=payload)
+
+    assert response.status_code == 422
+    assert response.json()["message"].startswith("validation error:")