How to implement pytest for FastAPI with MongoDB(Motor)

Question

I want to write tests for my FastAPI endpoints

example for my code:

from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()

@app.get("/todos")
async def get_todo_by_title(title: str,current_user: User = Depends(get_current_user))
    document = await collection.find_one({"title": title})
    return document

client = TestClient(app)

def test_get_todo_by_title():
    response = client.get("/todos")
    assert response.status_code == 200

What the best way to test my endpoints?

I want to use fake DB for testing, something like json file

db = {
todos: [...]
}

Answer 1

It is not the best option to use fake data from a JSON file. Instead, you can use a testing DB (based on the env you are running your app through), or any other DB (dev, stg, ..etc), and delete your test data after running all unit tests.

Here is how to simply apply the latter approach in FastAPI;

• Assume you have 3 simple tables (or collections) X, Y, and Z
• MongoDB is the DB service
• PyTest is the test engine

conftest.py

from pytest import fixture
from starlette.config import environ
from starlette.testclient import TestClient
from config.db_connection import database, X_collection, Y_collection, Z_collection


@fixture(scope="session")
def test_X():
    return {
        "_id": "10",
        "name": "test",
        "description": "test",
        "type": "single value",
        "crt_at": "2022-06-27T12:23:15.143Z",
        "upd_at": "2022-06-27T12:23:15.143Z"
    }

//test_Y and test_Z fixtures should be like test_X


@fixture(scope="session", autouse=True)
def test_client(test_X, test_Y, test_Z):
    import main
    application = main.app
    with TestClient(application) as test_client:
        yield test_client

    db = database
    //Here, delete any objects you have created for your tests
    db[X_collection].delete_one({"_id": test_X["_id"]})
    db[Y_collection].delete_one({"_id": test_Y["_id"]})
    db[Z_collection].delete_one({"_id": test_Z["_id"]})


environ['TESTING'] = 'TRUE'

Unit tests should look like the following sample.

test_X_endpoints.py

def test_create_X(test_client, test_X):
    response = test_client.post("/create_X_URI/", json=test_X)
    assert response.status_code == 201
    //Add assertions as needed

def test_list_X(test_client):
    response = test_client.get("/list_X_objects_URI/?page=1&size=1")
    assert response.status_code == 200
    //Add assertions as needed