Preserve response context testing flask app with pytest

Question

I'm testing a flask application with py.test with the following code:

response = flask_app_test_client.post('/users', data=json.dumps(user))
assert response.status_code == 201
assert response.content_type == 'application/json'
assert isinstance(response.json, dict)
assert set(response.json.keys()) >= {'id', 'status', 'created_at', 'updated_at'}
assert response.json['name'] == user['name']
assert response.json['status'] == 'pending'

When some assertion fails I'm getting something like this:

            response = test_client.post('/users', data=json.dumps(user))
    >       assert response.status_code == 201
    E       assert 400 == 201
    E        +  where 400 = <JSONResponse streamed [400 BAD REQUEST]>.status_code
    ============== 1 failed, 3 passed in 0.10 seconds ===================

I do a lot of TDD so I expect my test fails frequently while developing. My problem is the assertion error message is kind of useless without the rest of the response data (body, headers, etc).

I only get in the output that the response.status_code is 400 but I don't get the error description that is in the response body: {"errors": ["username is already taken", "email is required"]} . Ideally I would like a full dump of the request and response (headers + body) when an assertion fails.

How I can print a summary of the response on each failed assertion?

Answer 1

Assert statement graamar

assert response.status_code == 201, "Anything you want"

You can be as verbose as you want. You can also use UnitTest's suite of helper methods - without test case classes through this bit of abuse - https://github.com/nose-devs/nose2/blob/master/nose2/tools/such.py#L34

Answer 2

I'm came up with two different solutions.

Solution #1: try/catch

try:
    assert response.status_code == 201
    assert response.content_type == 'application/json'
    assert isinstance(response.json, dict)
    assert set(response.json.keys()) >= {'id', 'status', 'created_at', 'updated_at'}
    assert response.json['name'] == user['name']
    assert response.json['status'] == 'pending'
except AssertionError as e:
    except AssertionError as e:
    raise ResponseAssertionError(e, response)

class ResponseAssertionError(AssertionError):
    def __init__(self, e, response):
        response_dump = "\n +  where full response was:\n" \
                        "HTTP/1.1 {}\n" \
                        "{}{}\n".format(response.status, response.headers, response.json)

        self.args = (e.args[0] + response_dump,)

Solution #2: no try/catch needed (if repr is too long sometimes is cut off...)

Extend and override Flask response object

import json
class JSONResponse(Response):

    def __repr__(self):
        headers = {}
        while len(self.headers) > 0:
            tuple_ = self.headers.popitem()
            headers[tuple_[0]] = tuple_[1]

        data = {
            'status': self.status,
            'headers': headers,
            'body': self.json
        }
        return json.dumps(data)

and

    @pytest.fixture(scope='session')
    def test_client(flask_app):
        flask_app.response_class = JSONResponse
        return flask_app.test_client()

Answer 3

I know this is an older question, but Pytest has an option --pdb that will pop you into a PDB shell should your test fail. Very handy way to "just look around" rather than having to pass tons of stuff to an exception message.