Tests within a class do not share the same class object

Hey All,

I was surprised when I found out that Tests within a class do not share the same Class object. My use case is that I am trying to save some data to self from one test, and use it again in another test. Why does every test object get a separate instance of the Test Class. What is the point of wrapping tests within a class, if the instance of the class does not persist for all of the tests in the class?

Example:

import pytest
  
class MySuper():
    counter = 0

class TestA(MySuper):
    def test_1(self):
        print("Test 1")
        self.counter += 3
        print(self.counter)
        print(self)
        print(dir(self))

    def test_2(self):
        print("Test 2")
        self.counter += 2
        print(self.counter)
        print(self)
        print(dir(self))
        assert self.counter == 5

Output: (notice the memory addresses of self are different)

pytest -s
=================================================================================================================================== test session starts ===================================================================================================================================
platform linux -- Python 3.6.9, pytest-3.8.2, py-1.7.0, pluggy-0.7.1
rootdir: /home/e339307/pytest_tmp, inifile:
plugins: swte-2.0.0, mock-1.10.0
collected 2 items                                                                                                                                                                                                                                                                         

my_simple_test.py Test 1
3
<my_simple_test.TestA object at 0x7f8daad2ef28>
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'counter', 'test_1', 'test_2']
.Test 2
2
<my_simple_test.TestA object at 0x7f8daad2e7b8>
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'counter', 'test_1', 'test_2']
F

======================================================================================================================================== FAILURES =========================================================================================================================================
______________________________________________________________________________________________________________________________________ TestA.test_2 _______________________________________________________________________________________________________________________________________

self = <my_simple_test.TestA object at 0x7f8daad2e7b8>

    def test_2(self):
        print("Test 2")
        self.counter += 2
        print(self.counter)
        print(self)
        print(dir(self))
>       assert self.counter == 5
E       assert 2 == 5
E        +  where 2 = <my_simple_test.TestA object at 0x7f8daad2e7b8>.counter

my_simple_test.py:20: AssertionError
====================================================================================================================================== REQUIREMENTS =======================================================================================================================================
=========================================================================================================================== 1 failed, 1 passed in 0.08 seconds ============================================================================================================================

Thanks!
Seth

[Zac-HD]

What is the point of wrapping tests within a class?

Compatibility with the standard library unittest module, to allow gradual migrations to pytest's preferred test-function style!

[nicoddemus]

Also sometimes it makes sense to group tests in a class for organizational reasons, share fixtures only with tests within that class, apply marks in the class so they apply to all tests in the class... there are many reasons.

Is it documented anywhere that each test gets their own instance of the class? I was a little shocked when I figured that out.

I also think it would make sense to change the behavior so that every test within a class shared the same instance of the class.

[nicoddemus]

Hmm I don't think so, but is certainly worth doing it. Created #6900 to track this, thanks. 👍