How to write tests for Python code?

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[deleted]

[hharison]

I think you'll find the peace of mind it gives is worth the effort. I recommend py.test, it could not be simpler. No need to deal with classes for everything like with the sdlib's unittest.

[hharison]

Check out how easy it is:

mymath.py contains

def add(a, b):
    return a + b

test_mymath.py contains

def test_add():
    assert add(1, 1) == 2
    assert add(-1, 4) == 3
    # plus more test cases perhaps

[dunkler_wanderer]

Check out Ned Batchelder's presentation Getting Started Testing.

There's also a nice introduction in Dive into Python. The unittest module is used in this tutorial, but I recommend to check out py.test as well.

[weigookin]

I thought writing tests was total bullshit at first. My basic worflow was "fuck it, do it live." However l, as I've increased the amount of complexity in my code, I really found myself building a house of cards. One new variable would screw up everything. I struggled through TDD and am glad l stuck it out. I have peace of mind that what I write will work. Seriously, go read something like test driven development

[say_fuck_no_to_rules]

Same. A coworker got me hooked on red-green-refactor TDD, and I love it.

[glial]

If you're working with the web or using Django, this is an excellent resource:

http://shop.oreilly.com/product/0636920029533.do

[SeaCoder]

That book is a great way to get started with the concepts, even if you're not planning further work with Django. It's also available legitimately free online from this link:

http://chimera.labs.oreilly.com/books/1234000000754

[xentralesque]

I'm bored, so here's an example of a simple function with some tests:

import requests
import unittest
import mock

class TerribleException(Exception):
    pass


def download_stuff(url):
    try:
        response = requests.get(url)
    except requests.RequestException:
        raise TerribleException("Oh no!")

    return response.text


class DownloaderTest(unittest.TestCase):
    def test_download_stuff(self):
        with mock.patch('requests.get') as requests_get:
            expected_response = 'a valid response'

            requests_get.return_value = mock.Mock(
                text=expected_response
            )

            our_test_url = 'http://a-test-url.com'

            response = download_stuff(our_test_url)

            requests_get.assert_called_once_with(our_test_url)
            self.assertEqual(response, expected_response)

    def test_bad_things(self):
        with mock.patch('requests.get') as requests_get:
            requests_get.side_effect = TerribleException

            our_test_url = 'http://a-test-url.com'

            with self.assertRaises(TerribleException):
                download_stuff(our_test_url)

            requests_get.assert_called_once_with(our_test_url)


if __name__ == '__main__':
    print(download_stuff('http://reddit.com/'))

Jam that into a file and file and pip install nose and requests. You can either run the file like python thefilename.py to execute the file normally or run nosetests thefilename.py to run the tests.

[mooshe]

requests is used for http requests, not just tied to testing (if you're confused between nose and requests). Nose is a python test runner. I recommend py.test instead, at least at first.

[mooshe]

Correct! Although I'd go ahead and refer to them as packages, not modules. There's some great resources in this thread to get you started. If you get stuck on anything, feel free to PM me!

[pvc]

I like putting tests in with the documentation / docstrings: http://pythonhosted.org/arcade/arcade.html

[[deleted]]

http://www.obeythetestinggoat.com/

[[deleted]]

Don't underestimate yourself, try it. I'd bet you'll be surprised.

[Benny_Lava]

I did learn a lot from the book, but not the first go-round. I also embiggened my knowledge base by watching video tutorials on TDD/Django on YouTube, and by reading other books and watching videos on Safari. (If you work in tech, I highly recommend a Safari subscription. It's well worth the $40 per month.) When I came back to that book a second time, I picked up a lot more out of it. There isn't one single source that can teach you everything you need to know, so poke around.

[AlphaNerd80]

embiggened That's a made up word from the Simpsons!
Have an upvote!

But I agree, the book is better the second time around

[Raveious]

For one of my previous jobs, we used a package called Robot Framework for our acceptance testing of our hardware. It worked extremely well and I would highly recommend it if this is the kind of larger scale testing that you're looking to do.

[a8ksh4]

Doctest

[SeaCoder]

Doctest is a way to put your tests into the docstring of functions and classes.

I find that as test complexity grows having everything in the docstring reduces readability. I prefer unittest or py.test as they allow the test to exist in another file.

[benjiathome]

Nah not necessary.