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 i need to make to make this test code work?

2.Do i also have to patch 'urlparse'?

Solution 1

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

import mysql.connector
import os, urlparse


@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:

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


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


test_func()

Solution 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>)

Solution 3

In my use case, I was trying to mock having NO environmental variable set. To do that, make sure you add clear=True to your patch.

with patch.dict(os.environ, {}, clear=True):
    func()

Solution 4

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"

Solution 5

At the head of your file mock environ before importing your module:

with patch.dict(os.environ, {'key': 'mock-value'}):
    import your.module

View more solutions

Comments

[immrsteel]

Thanks man,i realized it later and soon after deleted my comment.Thanks a lot it is working but i am confused that using above method how {'mytemp':'mytemp'} getting passed into os.environ

[immrsteel]

Thanks a lot,I accepted the answer and will upvote the answer when i will have 15 reputation.

[Sonic Soul]

this gives me AttributeError: 'MockFixture' object has no attribute 'setenv'

[r44]

This works for me, using pytest==3.5.0. @SonicSoul maybe your version is different?

[Martin Thoma]

As it doesn't make a difference for the question / answer, I removed the wrong Python code from both :-)

[Calvin Li]

@SonicSoul make sure to include monkeypatch in the test arguments

[Andrew Vaccaro]

This is exactly what I was missing, thanks!

[Javi Torre]

Great answer!!!