Python mock Patch os.environ and return value

Question

Unit testing conn() using mock:

app.py

import mysql.connector
import os, urlparse


def conn():
    if "DATABASE_URL" in os.environ:
        url = urlparse(os.environ["DATABASE_URL"])
        g.db = mysql.connector.connect(
            user=url.username,
            password=url.password,
            host=url.hostname,
            database=url.path[1:],
        )
    else:
        return "Error"

test.py

def test_conn(self):
    with patch(app.mysql.connector) as mock_mysql:
        with patch(app.os.environ) as mock_environ:
            con()
            mock_mysql.connect.assert_callled_with("credentials")

Error: Assertion mock_mysql.connect.assert_called_with is not called.

which I believe it is because 'Database_url' is not in my patched os.environ and because of that test call is not made to mysql_mock.connect.

Questions:

1. What changes do I need to make this test code work?

2. Do I also have to patch urlparse?

Answer 1

You can try unittest.mock.patch.dict solution. Just call conn with a dummy argument:

import mysql.connector
import os, urlparse
from unittest import mock


@mock.patch.dict(os.environ, {"DATABASE_URL": "mytemp"}, clear=True)  # why need clear=True explained here https://stackoverflow.com/a/67477901/248616
def conn(mock_A):
    print os.environ["mytemp"]
    if "DATABASE_URL" in os.environ:
        url = urlparse(os.environ["DATABASE_URL"])
        g.db = mysql.connector.connect(
            user=url.username,
            password=url.password,
            host=url.hostname,
            database=url.path[1:],
        )
    else:
        return "Error"

Or if you don't want to modify your original function try this solution:

import os
from unittest import mock

def func():
    print os.environ["mytemp"]


def test_func():
    k = mock.patch.dict(os.environ, {"mytemp": "mytemp"})
    k.start()
    func()
    k.stop()


test_func()

Answer 2

For this, I find that pytest's monkeypatch fixture leads to better code when you need to set environment variables:

def test_conn(monkeypatch):
    monkeypatch.setenv('DATABASE_URL', '<URL WITH CREDENTIAL PARAMETERS>')
    with patch(app.mysql.connector) as mock_mysql:
        conn()
    mock_mysql.connect.assert_called_with(<CREDENTIAL PARAMETERS>)

Answer 3

The accepted answer is correct. Here's a decorator @mockenv to do the same.

def mockenv(**envvars):
    return mock.patch.dict(os.environ, envvars)


@mockenv(DATABASE_URL="foo", EMAIL="[email protected]")
def test_something():
    assert os.getenv("DATABASE_URL") == "foo"