How to make simulate_post work?

[phbelitz]

Hey there, I'm struggeling with setting up some test cases for my falcon app and can't quite make it work. Here my very simplified example server:

import json
import falcon

class Index:
    def on_post(self, req, rsp):
        content = json.load(req.stream)

        rsp.text = f"You got this: {str(json.dumps(content))}"
        rsp.content_type = "application/json"
        rsp.status = falcon.HTTP_200


def create():
    APP = falcon.App()
    APP.add_route("/", Index())
    return APP

This works fine. I run this with a cheroot wsgi server and get the expected response (all running in a container). Now I'm trying to setup a test case using pytest. Here the example:

import pytest
import app.falcon as fl
from falcon import testing


@pytest.fixture
def client():
    return testing.TestClient(fl.create())


def test_index(client):
    response = client.simulate_post("/", json={"hurr": "durr"})
    assert response.status_code == 200
    assert response.text == 'You got this: {"hurr": "durr"}'

This leads to the following error:

==================================================================================== test session starts =====================================================================================
platform linux -- Python 3.9.6, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /data
plugins: cov-2.10.1, asyncio-0.15.1, requests-mock-1.8.0, subprocess-1.0.1, mock-3.3.1
collected 1 item                                                                                                                                                                             

tests/test_falcon.py F                                                                                                                                                                 [100%]Coverage.py warning: Module connaisseur was never imported. (module-not-imported)
Coverage.py warning: No data was collected. (no-data-collected)
WARNING: Failed to generate report: No data to report.

/usr/local/lib/python3.9/site-packages/pytest_cov/plugin.py:271: PytestWarning: Failed to generate report: No data to report.

  self.cov_controller.finish()


========================================================================================== FAILURES ==========================================================================================
_________________________________________________________________________________________ test_index _________________________________________________________________________________________

client = <falcon.testing.client.TestClient object at 0x7f97e001a850>

    def test_index(client):
        response = client.simulate_post("/", json={"hurr": "durr"})
>       assert response.status_code == 200
E       assert 500 == 200
E        +  where 500 = <falcon.testing.client.Result object at 0x7f97e001af70>.status_code

tests/test_falcon.py:13: AssertionError
------------------------------------------------------------------------------------ Captured stderr call ------------------------------------------------------------------------------------
2021-10-12 15:47:45 [FALCON] [ERROR] POST / => Traceback (most recent call last):
  File "falcon/app.py", line 361, in falcon.app.App.__call__
  File "/usr/local/lib/python3.9/site-packages/app/falcon.py", line 6, in on_post
    content = json.load(req.stream)
  File "/usr/local/lib/python3.9/json/__init__.py", line 293, in load
    return loads(fp.read(),
  File "/usr/local/lib/python3.9/wsgiref/validate.py", line 197, in read
    assert_(len(args) == 1)
  File "/usr/local/lib/python3.9/wsgiref/validate.py", line 128, in assert_
    raise AssertionError(*args)
AssertionError


----------- coverage: platform linux, python 3.9.6-final-0 -----------

================================================================================== short test summary info ===================================================================================
FAILED tests/test_falcon.py::test_index - assert 500 == 200
===================================================================================== 1 failed in 0.18s ======================================================================================

Obvious question now ... what am I doing wrong?

[vytas7]

Hi @phbelitz!
In order to simulate requests without going over the network, Falcon's test client uses wsgiref's machinery, which has some glitches in its input stream wrapper (you might observe a similar behavior using wsgiref.simple_server). This is discussed more in depth here: req.stream. See also: Why does req.stream.read() hang for certain requests?

In order to make your code work on any PEP-3333 compliant WSGI server regardless of the underlying implementation, you can instead use our req.bounded_stream wrapper, which works around the most common differences in WSGI input stream behavior.

The following passes for me:

import json

import falcon
import pytest
from falcon import testing


class Index:
    def on_post(self, req, rsp):
        content = json.load(req.bounded_stream)

        rsp.text = f"You got this: {str(json.dumps(content))}"
        rsp.content_type = "application/json"
        rsp.status = falcon.HTTP_200


def create():
    APP = falcon.App()
    APP.add_route("/", Index())
    return APP


@pytest.fixture
def client():
    return testing.TestClient(create())


def test_index(client):
    response = client.simulate_post("/", json={"hurr": "durr"})
    assert response.status_code == 200
    assert response.text == 'You got this: {"hurr": "durr"}'

collected 1 item                                                                                      

test.py::test_index PASSED                                                                      [100%]

========================================== 1 passed in 0.13s ==========================================

P.S. You might also check our Internet media handling features to reduce the amount of manual wrangling of serialization and deserialization.
For instance, I could simplify your example somewhat as:

import json

import falcon
import pytest
from falcon import testing


class Index:
    def on_post(self, req, resp):
        content = req.get_media()
        resp.media = {'info': f"You got this: {json.dumps(content)}"}


def create():
    app = falcon.App()
    app.add_route("/", Index())
    return app


@pytest.fixture
def client():
    return testing.TestClient(create())


def test_index(client):
    response = client.simulate_post("/", json={"hurr": "durr"})
    assert response.status_code == 200
    assert response.json == {'info': 'You got this: {"hurr": "durr"}'}

[phbelitz]

perfect thank you.