TopolearnFixtures remove duplicated setup and guarantee that temp files, servers and patches are cleaned up.
Fixtures prepare the world a test needs and tear it down afterwards.
setUp(self)runs before each test method;tearDown(self)after each, even if the test failed (but not ifsetUpitself raised).setUpClass(cls)/tearDownClass(cls), decorated with@classmethod, run once per class. Use them for expensive, read-only resources such as a database schema. Shared mutable state between tests causes order-dependent failures.setUpModule()/tearDownModule()are functions at module level for once-per-file setup.
Cleanups are more robust than tearDown. self.addCleanup(func, *args) registers a function to call after the test; cleanups run in reverse order (LIFO) and run even if setUp failed after registering them. Register each cleanup right after acquiring the resource.
self.enterContext(cm) (3.11+) enters a context manager and registers its exit as a cleanup, returning the __enter__ result. That works for temp directories, open files and mock.patch:
self.tmp = self.enterContext(tempfile.TemporaryDirectory())addClassCleanup / enterClassContext are the class-level equivalents.
Example
import tempfile, unittest
from pathlib import Path
class TestNotes(unittest.TestCase):
@classmethod
def setUpClass(cls):
print("setUpClass once")
def setUp(self):
self.dir = Path(self.enterContext(tempfile.TemporaryDirectory()))
self.file = self.dir / "notes.txt"
self.file.write_text("hello")
self.addCleanup(print, "cleanup for", self._testMethodName)
def test_read(self):
self.assertEqual(self.file.read_text(), "hello")
def test_append(self):
with self.file.open("a") as f:
f.write("!")
self.assertEqual(self.file.read_text(), "hello!")
unittest.main(exit=False)
# setUpClass once / cleanup for test_append / cleanup for test_read
# Ran 2 tests ... OKRemember
- setUp/tearDown run around every test; setUpClass once per class
- addCleanup runs LIFO, even after failures in setUp
- enterContext(cm) enters a context manager and schedules its exit
Watch out for
- Mutating objects created in setUpClass, so tests pass or fail depending on order.