Develop Reference

FastAPI POST Pydantic method unit testing redirecting status_code 307 instead of 200

I have a test case where I am testing a POST service using pytest hosted with FastAPI Uvicorn. However the response is getting responded with status code 307. But this doesn't happen on actual webservice is tested through a browser or curl. What is happening here?
from fastapi.testclient import TestClient
from src.main import app
import json
client = TestClient(app)
def test_get_confidence_ws():
data = {
"acc_id": 1234567801,
"remoteIp": "127.255.255.255",
"userAgent": "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:104.0) Gecko/20100101 Firefox/104.0"
}
response = client.post("/confidence", json=json.dumps(data))
assert response.status_code == 200
Test response
> assert response.status_code == 200
E assert 307 == 200
E + where 307 = <Response [307]>.status_code
EDIT:
Actual endpoint that is tested:
#app.post("/confidence/")
def get_confidence(json: LoginClassifierSchema):
...
response = {
"key" : "value"
}
return response

Thanks #MatsLindh and #Vaizki for your responses. The problem was indeed with / and Validation. I will explain in detail so as this benefits the community.
1>If you are getting redirected to 307 this is indeed you have an extra '/' in the endpoint.
2>If you are getting 422 it is most likely a parsing issue. In my case I was using pydantic and though pydantic models are dictionary like, they are not dictionaries. Therefore to get the exact keys you need to convert the data at endpoint to a dictionary by calling data.dict(). eg.,
#app.post("/confidence")
def get_confidence(data: LoginClassifierSchema):
data = data.dict()
...
...
return JSONResponse({"key":"val"}, status_code=200)
In order to understand at an early stage it is a validation issue, add a exception handler method to your app class with endpoints.
from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse
from fastapi.exceptions import RequestValidationError
#app.exception_handler(RequestValidationError)
async def validation_exception_handler(request: Request, exc: RequestValidationError):
"""
This catches the schema validation error made during the call
"""
validation_err = {"exception": "RequestValidationError: unable to parse input, " + str(exc)}
return JSONResponse(validation_err, status_code=400)

Unit Testing Replace remote API Server with predefined response

So, I have a server running FastAPI which will make a API call to a remote API upon request.
I am developping unit-testing for this application, but here comes the question:
Can I, for the purpose of the test, replace a legit remote API server response by a predefined response ?
Example of the tests runned:
from fastapi.testclient import TestClient
from web_api import app
client = TestClient(app)
def test_get_root():
response = client.get('/')
assert response.status_code == 200
assert response.json() == {"running": True}
And the my server
from fastapi import FastAPI
app = FastAPI()
#app.get("/")
def home():
return {"running": True}
This is a simple example, but on other endpoints of my API I would call an external remote API
def call_api(self, endpoint:str, params:dict):
url = self.BASEURL + urllib.parse.quote(endpoint)
try:
response = requests.get(url, params=params)
response.raise_for_status()
except requests.exceptions.HTTPError as error:
print(error)
return response
Because I want to test the response of MY API, I would like to replace the remote API with a predefined response.
Also, one user request can end-up in multiple background API requests with transformed pieces of data.
Edit
Here are some more details on the structure of the application:
#app.get("/stuff/.......",
# lots of params
)
def get_stuff_from_things(stuff:list, params):
api = API(api_key=...)
# Do some stuff with the params
things = generate_things_list(params)
api.search_things(params)
# Check the result
# do some other stuff
return some_response
class API:
BASE_URL = 'https://api.example.com/'
def search_things(self, params):
# Do some stuff
# like putting stuff in the params
for s in stuff:
s.update(self.get_thing(params)) # -> get_thing()
# Do some more stuff
return stuff
# get_thing <- search_things
def get_thing(self, params...):
# Some stuff
results = self.call_api('something', params) # -> call_api()
json = results.json()
# Some more stuff
things = []
for thing in json['things']:
t = Thing(thing)
things.append(t)
return things
# call_api <- get_thing
def call_api(self, endpoint:str, params:dict):
url = self.BASEURL + urllib.parse.quote(endpoint)
try:
response = requests.get(url, params=params)
response.raise_for_status()
except requests.exceptions.HTTPError as error:
print(error)
self.last_response = response
return response
Nb. That is pseudo-code, I simplified the functions by removing the parameters, etc.
I hope it is clear, thanks for your help.

A complex API method might look like this (please pay attention to the depends mechanism - it is crucial):
import urllib
import requests
from fastapi import FastAPI, Depends
app = FastAPI()
# this can be in a different file
class RemoteCallWrapper:
def call_api(self, baseurl: str, endpoint: str, params: dict):
url = baseurl + urllib.parse.quote(endpoint)
try:
response = requests.get(url, params=params)
response.raise_for_status()
except requests.exceptions.HTTPError as error:
print(error)
return response
#app.get("/complex_api")
def calls_other_api(remote_call_wrapper=Depends(RemoteCallWrapper)):
response = remote_call_wrapper.call_api("https://jsonplaceholder.typicode.com",
"/todos/1", None)
return {"result": response.json()}
Now, we wish to replace the remote call class. I wrote a helper library that simplifies the replacement for tests - pytest-fastapi-deps:
from fastapi.testclient import TestClient
from mock.mock import Mock
from requests import Response
from web_api import app, RemoteCallWrapper
client = TestClient(app)
class MyRemoteCallWrapper:
def call_api(self, baseurl: str, endpoint: str, params: dict):
the_response = Mock(spec=Response)
the_response.json.return_value = {"my": "response"}
return the_response
def test_get_root(fastapi_dep):
with fastapi_dep(app).override({RemoteCallWrapper: MyRemoteCallWrapper}):
response = client.get('/complex_api')
assert response.status_code == 200
assert response.json() == {"result": {"my": "response"}}
You override the RemoteCallWrapper with your MyRemoteCallWrapper implementation for the test, which has the same spec.
As asserted - the response changed to our predefined response.

It sounds like you'd want to mock your call_api() function.
With a small modification to call_api() (returning the result of .json()), you can easily mock the whole function while calling the endpoint in your tests.
I'll use two files, app.py and test_app.py, to demonstrate how I would do this:
# app.py
import requests
import urllib
from fastapi import FastAPI
app = FastAPI()
def call_api(self, endpoint: str, params: dict):
url = self.BASEURL + urllib.parse.quote(endpoint)
try:
response = requests.get(url, params=params)
response.raise_for_status()
except requests.exceptions.HTTPError as error:
print(error)
return response.json() # <-- This is the only change. Makes it easier to test things.
#app.get("/")
def home():
return {"running": True}
#app.get("/call-api")
def make_call_to_external_api():
# `endpoint` and `params` could be anything here and could be different
# depending on the query parameters when calling this endpoint.
response = call_api(endpoint="something", params={})
# Do something with the response...
result = response["some_parameter"]
return result
# test_app.py
from unittest import mock
from fastapi import status
from fastapi.testclient import TestClient
import app as app_module
from app import app
def test_call_api_endpoint():
test_response = {
"some_parameter": "some_value",
"another_parameter": "another_value",
}
# The line below will "replace" the result of `call_api()` with whatever
# is given in `return_value`. The original function is never executed.
with mock.patch.object(app_module, "call_api", return_value=test_response) as mock_call:
with TestClient(app) as client:
res = client.get("/call-api")
assert res.status_code == status.HTTP_200_OK
assert res.json() == "some_value"
# Make sure the function has been called with the right parameters.
# This could be dynamic based on how the endpoint has been called.
mock_call.assert_called_once_with(endpoint="something", params={})
If app.py and test_app.py are in the same directory you can run the tests simply by running pytest inside that directory.

Fast API with pytest using AsyncClient gives 422 on post?

I'm trying to send a request to an api using pytest through httpx.AsynClient
#pytest.mark.anyio
async def test_device_create_with_data(self, client, random_uuid):
device_create = DeviceCreateFactory.build(subId=random_uuid)
json = device_create.json(by_alias=True)
response = await client.post("/device", json=json)
assert response.status_code == 200
Client fixture:
from httpx import AsyncClient
#pytest.fixture(scope="session")
async def client():
async with AsyncClient(
app=app,
base_url="http://test/api/pc",
headers={"Content-Type": "application/json"}
) as client:
yield client
API endpoint:
#device_router.post("/device", response_model=CommonResponse)
async def create_device(device: DeviceCreate):
_, err = await crud_device.create_device(device)
if err:
return get_common_response(400, err)
return get_common_response(200, "ok")
Schemas:
class DeviceBase(BaseModel):
device_id: StrictStr = Field(..., alias='deviceId')
device_name: StrictStr = Field(..., alias='deviceName')
device_type: StrictStr = Field(..., alias='deviceType')
age_mode: AgeModeType = Field(..., alias='ageMode')
class Config:
allow_population_by_field_name = True
validate_all = True
validate_assignment = True
class DeviceCreate(DeviceBase):
sub_id: StrictStr = Field(..., alias='subId')
class Config:
orm_mode = True
Factory:
from pydantic_factories import ModelFactory
from app.core.schemas.device import DeviceCreate
class DeviceCreateFactory(ModelFactory):
__model__ = DeviceCreate
And i'm getting a 422 error with following response content:
"message":"bad request","details":{"deviceId":"field required","deviceName":"field required","deviceType":"field required","ageMode":"field required","subId":"field required"}
Then i examined the data of the request being sent and got:
b'"{\\"deviceId\\": \\"de\\", \\"deviceName\\": \\"\\", \\"deviceType\\": \\"\\", \\"ageMode\\": \\"child\\", \\"subId\\": \\"11aded61-9966-4be1-a781-387f75346811\\"}"'
Seems like everything is okay, but where is the trouble then?
I've tried to examine the request data in exception handler of 422
I've made:
#app.exception_handler(RequestValidationError)
async def validation_exception_handler(request: Request, exc: RequestValidationError):
print(await request.json())
response = validation_error_response(exc)
return JSONResponse(
status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
content=jsonable_encoder(response.dict())
)
But code after print is unreachable, because await request.json() never ends and runs forever trying to print a request json
Is there a way to manage this problem?
Thanks for any suggest!
P.S.
python version: 3.8.9
fastapi version: 0.68.1
httpx version: 0.21.1

You're double encoding your content as JSON - you're both asking for it to be returned as a JSON string, and then telling your request method to encode it as JSON a second time. json= as an argument to the method on the client converts the given data to JSON - it does not expect already serialized JSON.
You can see this in your request string because it starts with " and not with { as you'd expect:
b'"{\
^
Instead build your model around a dictionary - or as I'd prefer in a test - build the request by hand, so that you're testing how you imagine an actual request should look like.
You can use dict in the same was as you'd use json for a Pydantic model:
device_create = DeviceCreateFactory.build(subId=random_uuid)
response = await client.post("/device", json=device_create.dict(by_alias=True))
assert response.status_code == 200

Python - mock function and assert exception

I built an API with FastAPI that interacts with DynamoDB.
In the beginning of my journey in Test Driven Development, I have doubts about what to mock.
This is the get method, main.py:
router = FastAPI()
#router.get("/{device_id}")
def get_data(request: Request, device_id: str, query: DataQuery = Depends(DataQuery.depends)):
da_service = DaService()
try:
start_time, end_time = DaService.validate_dates(query.start, query.end)
return 'OK'
except WrongDataFormat as e:
raise HTTPException(status_code=400, detail=str(e))
except Exception as e:
raise HTTPException(status_code=500, detail='Internal Server Error')
In the test file I started by creating the success test, test_main.py:
from fastapi.testclient import TestClient
from unittest import mock
from utils.exceptions import WrongDataFormat
from endpoints.datalake import router
client = TestClient(router)
def test_success_response():
with mock.patch('endpoints.datalake.DataApiService.get_datalake_data'):
response = client.get('/xxxxx', params = {'start': '1629886483', 'end': '1629886504'})
assert response.status_code == 200
assert isinstance(response.json(), dict)
Now I want to create the test for when the exception WrongDataFormat is returned, but I'm not succeeding... This is what I have right now:
def test_exception_response_():
response = client.get('/xxxxx', params = {'2021-08-28', 'end': '2021-12-25'})
assert response.status_code == 400
How can I mock the function main.validate_dates to return the exception WrongDataFormat and assert it correctly?

If you want to test the status code and message of a response you have to use TestClient(app) where app is the FastAPI application. Converting the exception into the appropriate response is the task of the application, not the router (which is what you're testing with).
client = TestClient(app)
This way you can test the API of your application (which is the most useful surface to test, imho).

How to test that a model was used in a FastAPI route?

I'm trying to check if a specific model was used as an input parser for a FastAPI route. However, I'm not sure how to patch (or spy on) it.
I have the following file structure:
.
└── roo
├── __init__.py
├── main.py
└── test_demo.py
main.py:
from fastapi import FastAPI
from pydantic import BaseModel
app = FastAPI()
class ItemModel(BaseModel):
name: str
#app.post("/")
async def read_main(item: ItemModel):
return {"msg": f"Item: {item.name}"}
test_demo.py:
from fastapi.testclient import TestClient
from unittest.mock import patch
from roo.main import app, ItemModel
client = TestClient(app)
def test_can_creating_new_item_users_proper_validation_model():
with patch('roo.main.ItemModel', wraps=ItemModel) as patched_model:
response = client.post("/", json={'name': 'good'})
assert response.status_code == 200
assert response.json() == {"msg": "Item: good"}
assert patched_model.called
However, patched_model is never called (other asserts pass). I don't want to change the functionality or replace ItemModel in main.py, I just want to check if it was used.

My first approach to this was to wrap the read_main method and check that the item passed into the function is indeed an instance of ItemModel. But that was a dead-end approach because of the way FastAPI endpoints are prepared and stored: FastAPI stores a copy of the endpoint function objects in a list: (see fastapi/routing.py), then evaluates at request-time which endpoint to call.
from roo.main import app
def test_read_main():
assert 'read_main' in [r.endpoint.__name__ for r in app.routes]
# check that read_main was called *and* received an ItemModel instance?
My second approach involves spying or "breaking" the initialization of ItemModel, such that if the endpoint does indeed use that model, then a "broken" ItemModel would cause a request that hits that endpoint to fail. We "break" ItemModel by making use of the fact that (1) FastAPI calls the __init__ of your model during the request-response cycle, and (2) a 422 error response is propagated by default when the endpoint is unable to serialize a model properly:
class ItemModel(BaseModel):
name: str
def __init__(__pydantic_self__, **data: Any) -> None:
print("Make a POST request and confirm that this is printed out")
super().__init__(**data)
So in tests, just mock the __init__ method:
Example for pytest
import pytest
from fastapi.testclient import TestClient
from roo.main import app, ItemModel
def test_read_main(monkeypatch: pytest.MonkeyPatch):
client = TestClient(app)
def broken_init(self, **data):
pass # `name` and other fields won't be set
monkeypatch.setattr(ItemModel, '__init__', broken_init)
with pytest.raises(AttributeError) as exc:
client.post("/", json={'name': 'good'})
assert 422 == response.status_code
assert "'ItemModel' object has no attribute" in str(exc.value)
Example for pytest + pytest-mock's mocker.spy
from fastapi.testclient import TestClient
from pytest_mock import MockerFixture
from roo.main import app, ItemModel
def test_read_main(mocker: MockerFixture):
client = TestClient(app)
spy = mocker.spy(ItemModel, '__init__')
client.post("/", json={'name': 'good'})
spy.assert_called()
spy.assert_called_with(**{'name': 'good'})
Example for unittest
from fastapi.testclient import TestClient
from roo.main import app, ItemModel
from unittest.mock import patch
def test_read_main():
client = TestClient(app)
# Wrapping __init__ like this isn't really correct, but serves the purpose
with patch.object(ItemModel, '__init__', wraps=ItemModel.__init__) as mocked_init:
response = client.post("/", json={'name': 'good'})
assert 422 == response.status_code
mocked_init.assert_called()
mocked_init.assert_called_with(**{'name': 'good'})
Again, the tests check that the endpoint fails in either serializing into an ItemModel or in accessing item.name, which will only happen if the endpoint is indeed using ItemModel.
If you modify the endpoint from item: ItemModel into item: OtherModel:
class OtherModel(BaseModel):
name: str
class ItemModel(BaseModel):
name: str
#app.post("/")
async def read_main(item: OtherModel): # <----
return {"msg": f"Item: {item.name}"}
then running the tests should now fail because the endpoint is now creating the wrong object:
def test_read_main(mocker: MockerFixture):
client = TestClient(app)
spy = mocker.spy(ItemModel, '__init__')
client.post("/", json={'name': 'good'})
> spy.assert_called()
E AssertionError: Expected '__init__' to have been called.
test_demo_spy.py:11: AssertionError
with pytest.raises(AttributeError) as exc:
response = client.post("/", json={'name': 'good'})
> assert 422 == response.status_code
E assert 422 == 200
E +422
E -200
test_demo_pytest.py:15: AssertionError
The assertion errors for 422 == 200 is a bit confusing, but it basically means that even though we "broke" ItemModel, we still got a 200/OK response.. which means ItemModel is not being used.
Likewise, if you modified the tests first and mocked-out the __init__ of OtherModel instead of ItemModel, then running the tests without modifying the endpoint will result in similar failing tests:
def test_read_main(mocker: MockerFixture):
client = TestClient(app)
spy = mocker.spy(OtherModel, '__init__')
client.post("/", json={'name': 'good'})
> spy.assert_called()
E AssertionError: Expected '__init__' to have been called.
def test_read_main():
client = TestClient(app)
with patch.object(OtherModel, '__init__', wraps=OtherModel.__init__) as mocked_init:
response = client.post("/", json={'name': 'good'})
# assert 422 == response.status_code
> mocked_init.assert_called()
E AssertionError: Expected '__init__' to have been called.
The assertion here is less confusing because it says we expected that the endpoint will call OtherModel's __init__, but it wasn't called. It should pass after modifying the endpoint to use item: OtherModel.
One last thing to note is that since we are manipulating the __init__, then it can cause the "happy path" to fail, so it should now be tested separately. Make sure to undo/revert the mocks and patches:
Example for pytest
def test_read_main(monkeypatch: pytest.MonkeyPatch):
client = TestClient(app)
def broken_init(self, **data):
pass
# Are we really using ItemModel?
monkeypatch.setattr(ItemModel, '__init__', broken_init)
with pytest.raises(AttributeError) as exc:
response = client.post("/", json={'name': 'good'})
assert 422 == response.status_code
assert "'ItemModel' object has no attribute" in str(exc.value)
# Okay, really using ItemModel. Does it work correctly?
monkeypatch.undo()
response = client.post("/", json={'name': 'good'})
assert response.status_code == 200
assert response.json() == {"msg": "Item: good"}
Example for pytest + pytest-mock's mocker.spy
from pytest_mock import MockerFixture
from fastapi.testclient import TestClient
from roo.main import app, ItemModel
def test_read_main(mocker: MockerFixture):
client = TestClient(app)
# Are we really using ItemModel?
spy = mocker.spy(ItemModel, '__init__')
client.post("/", json={'name': 'good'})
spy.assert_called()
spy.assert_called_with(**{'name': 'good'})
# Okay, really using ItemModel. Does it work correctly?
mocker.stopall()
response = client.post("/", json={'name': 'good'})
assert response.status_code == 200
assert response.json() == {"msg": "Item: good"}
Example for unittest
def test_read_main():
client = TestClient(app)
# Are we really using ItemModel?
with patch.object(ItemModel, '__init__', wraps=ItemModel.__init__) as mocked_init:
response = client.post("/", json={'name': 'good'})
assert 422 == response.status_code
mocked_init.assert_called()
mocked_init.assert_called_with(**{'name': 'good'})
# Okay, really using ItemModel. Does it work correctly?
response = client.post("/", json={'name': 'good'})
assert response.status_code == 200
assert response.json() == {"msg": "Item: good"}
All in all, you might want to consider if/why it's useful to check for which model is exactly used. Normally, I just check that passing-in valid request params returns the expected valid response, and likewise, that invalid requests returns an error response.