Explain the "setUp" and "tearDown" Python methods used in test cases

Question

Can anyone explain the use of Python's setUp and tearDown methods while writing test cases apart from that setUp is called immediately before calling the test method and tearDown is called immediately after it has been called?

Answer 1

In general you add all prerequisite steps to setUp and all clean-up steps to tearDown.

You can read more with examples here.

When a setUp() method is defined, the test runner will run that method prior to each test. Likewise, if a tearDown() method is defined, the test runner will invoke that method after each test.

For example you have a test that requires items to exist, or certain state - so you put these actions(creating object instances, initializing db, preparing rules and so on) into the setUp.

Also as you know each test should stop in the place where it was started - this means that we have to restore app state to it's initial state - e.g close files, connections, removing newly created items, calling transactions callback and so on - all these steps are to be included into the tearDown.

So the idea is that test itself should contain only actions that to be performed on the test object to get the result, while setUp and tearDown are the methods to help you to leave your test code clean and flexible.

You can create a setUp and tearDown for a bunch of tests and define them in a parent class - so it would be easy for you to support such tests and update common preparations and clean ups.

If you are looking for an easy example please use the following link with example

Answer 2

You can use these to factor out code common to all tests in the test suite.

If you have a lot of repeated code in your tests, you can make them shorter by moving this code to setUp/tearDown.

You might use this for creating test data (e.g. setting up fakes/mocks), or stubbing out functions with fakes.

If you're doing integration testing, you can use check environmental pre-conditions in setUp, and skip the test if something isn't set up properly.

For example:

class TurretTest(unittest.TestCase):

    def setUp(self):
        self.turret_factory = TurretFactory()
        self.turret = self.turret_factory.CreateTurret()

    def test_turret_is_on_by_default(self):
        self.assertEquals(True, self.turret.is_on())

    def test_turret_turns_can_be_turned_off(self):
        self.turret.turn_off()
        self.assertEquals(False, self.turret.is_on())

Answer 3

Suppose you have a suite with 10 tests. 8 of the tests share the same setup/teardown code. The other 2 don't.

setup and teardown give you a nice way to refactor those 8 tests. Now what do you do with the other 2 tests? You'd move them to another testcase/suite. So using setup and teardown also helps give a natural way to break the tests into cases/suites