fixture is a function used to provide preset environment or data for tests. 1. Use the @pytest.fixture decorator to define fixture; 2. Inject fixture in the form of parameters in the test function; 3. Execute setup before yield, and then teardown; 4. Control the scope through scope parameters, such as function, module, etc.; 5. Place the shared fixture in conftest.py to achieve cross-file sharing, thereby improving the maintainability and reusability of the test.
When testing with pytest , fixture is a very powerful feature to provide preset test environment or data for test functions. Below is a simple but complete pytest fixture example to help you understand how to define and use fixture.
? Basic fixture example: Database connection simulation
Suppose we want to test a module that operates "user data" and need a database connection object.
# test_user.py
import pytest
# Simulate database class Database:
def __init__(self):
self.users = {}
def add_user(self, user_id, name):
self.users[user_id] = name
def get_user(self, user_id):
return self.users.get(user_id)
def clear(self):
self.users.clear()
# Define fixture: Provide a clean database instance @pytest.fixture
def db():
print("\n[Setup] Create a database instance") # You can see the execution order database = Database()
yield database # Return to the test function to use print("[Teardown] to clean the database")
database.clear()
# Test cases use fixture
def test_add_user(db):
db.add_user(1, "Alice")
assert db.get_user(1) == "Alice"
def test_get_user_not_exists(db):
assert db.get_user(99) is None
def test_add_multiple_users(db):
db.add_user(1, "Alice")
db.add_user(2, "Bob")
assert len(db.users) == 2
assert db.get_user(2) == "Bob"? Run the test
Make sure you have pytest installed:
pip install pytest
Run the test:
pytest test_user.py -v
The output is similar:
test_user.py::test_add_user[Setup] Create a database instance PASSED[Teardown] Clean the database test_user.py::test_get_user_not_exists[Setup] Create a database instance PASSED[Teardown] Clean the database test_user.py::test_add_multiple_users[Setup] Create a database instance PASSED[Teardown] Clean the database
Each test function gets an independent db instance because the fixture function is re-executed before each test.
? fixture scope (scope)
You can control the multiplexing range of fixture, such as having multiple tests share the same instance:
@pytest.fixture(scope="module")
def db():
print("\n[Module Setup] Create database once")
database = Database()
yield database
print("[Module Teardown] Clean the database once")
database.clear()-
scope="function": By default, each test function is called once (most common) -
scope="class": Each test class is called once -
scope="module": Called once per.pyfile -
scope="session": The entire test session is only executed once
? conftest.py: Shared fixture
If you have multiple test files that need to use the same fixture, you can put it in conftest.py :
# conftest.py
import pytest
@pytest.fixture
def db():
database = Database()
yield database
database.clear() In this way, all test files in the same directory or subdirectories can be directly used with db without importing.
? Summarize the key points
-
@pytest.fixturedecorator defines reusable test resources -
yieldis setup before, then teardown -
fixturefunction name is passed into the test function as a parameter and automatically injected. - Implement cross-file sharing fixture using
conftest.py - The life cycle can be controlled through
scopeto improve performance
Basically that's it. fixture makes testing cleaner, reusable and easy to maintain.
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