pytest is awesome

pytest has been on my radar for quite a while and I tentatively used it in some project as a simple replacement for Python’s built-in unittest-module mostly because of awesome assertion output and because I hate to remember 100 different assertXYZ methods. But it became much more during the last couple of days.

Last Saturday, as part of the sprints at EuroPython 2013, Holger Krekel gave those of us new to the framework a set of slides and helped us to get to know it better. Big thanks for that! Since then I’ve become convinced that py.test is basically the only testing framework I want to use for all my future Python projects (well, until something even more awesome comes around).

As I said, I’ve only used the basics before and never got to stuff like fixtures and markers, but since last Saturday I have to wonder, how no other framework I’ve found so far has the -m flag (for selecting tests to run based on the markers they’ve got) and the -k flag for generally selecting tests by name.

> cat
import pytest

def test_a():
    assert 1 == 1

def test_b():
    assert 1 == 1

> py.test -m "unit" --collectonly
=== test session starts =======================
platform darwin -- Python 2.7.4 -- pytest-2.3.5
plugins: cov
collected 2 items
<Module ''>
  <Function 'test_b'>

=== 1 tests deselected by "-m 'unit'" =========
=== 1 deselected in 0.01 seconds ==============

As you can see in the example about, once test has been marked as “unit”, you can select it with -m "unit".

Also, injecting preconditions and helpers with fixtures just feels so much more natural than “beforeEach”/“setUp”-style methods.

def mock_service():
    # ...
    return service

def test_feature_a(mock_service):
    assert mock_service.do_something() == 'as_expected'

Digging into this stuff and also the “scope”-setting for fixtures was tons of fun and I really miss all these little things whenever I have to work with other testing frameworks (as much as I’ve come to love mocha + chai on the JavaScript side of things).

Next, I will probably try to learn more about how to integrate pytest better with Django using pytest-django, which was also demonstrated at this year’s EuroPython in Florence by Andreas Pelme.

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