pytest fixture scope

Scope controls how often a fixture gets called.

The default is “function”.

Here are the options for scope:

scope	When setup and teardown run
function	(default) Setup before each function, teardown after each function
class	Setup before first test of class, teardown after last test of class
module	Setup/Teardown bracketing tests of a module
package	Setup/Teardown bracketing tests of a package/directory
session	Setup/Teardown at the beginning and end of the entire test session / test run

Since the default scope is “function”, the cheese db example will open and close the db for every test.

Here’s the fixture again:

@pytest.fixture()
def cheese_db(request):
    # setup
    print('\n[setup] cheese_db, connect to db')

    # code to connect to your db 
    makeshift_cheese_db = {'Brie': 'No.', 'Camenbert': 'Ah! We have Camenbert, yessir.'}

    # return db to test code
    return makeshift_cheese_db

    # return db to test code
    yield makeshift_cheese_db
    
    # teardown
    print('\n[teardown] cheese_db, disconnect to db')

When run, we can see the setup/teardown once per function:

(cheese) $ pytest test_cheese.py -s
================== test session starts ==================
collected 3 items                                       

test_cheese.py 
[setup] cheese_db, connect to db
in test_brie()
.
[teardown] cheese_db, disconnect to db

[setup] cheese_db, connect to db
in test_camenbert()
.
[teardown] cheese_db, disconnect to db
=================== 3 passed in 0.04s ===================

This doesn’t really make sense. Especially if connecting is a time consuming operation.

Let’s change the scope to “module” so we only connect/disconnect from the db once per test file/module:

@pytest.fixture(scope="module")
def cheese_db(request):
  ...

And let’s re-run it:

$ pytest test_cheese.py -s
================== test session starts ==================
collected 3 items                                       

test_cheese.py 
[setup] cheese_db, connect to db
in test_brie()
.in test_camenbert()
.
[teardown] cheese_db, disconnect to db

=================== 3 passed in 0.04s ===================

There. Much better. The db is connected before it’s needed, and closed when we’re done with it.

This post is part of a series on pytest fixtures

pytest fixture return value

Parametrizing pytest fixtures with params

pytest fixture scope

pytest fixture return value

Parametrizing pytest fixtures with params

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