Fixtures in unittest

Introduction to Testing in Python

Alexander Levin

Data Scientist

Fixtures recap

Fixture
- a prepared environment for a test
- separate the preparation from the test code
Fixture setup - setting up resources for tests
Fixture teardown - cleaning up ("tearing down") resources that were allocated
Example: preparing the food for a picnic and the cleaning at the end

Fixtures in the unittest library

Fixture in unittest - the preparaton needed to perform one or more tests
.setUp() - a method called to prepare the test fixture before the actual test
.tearDown() - a method called after the test method to clean the environment

¹ https://docs.python.org/3/library/unittest.html

Example code

import unittest

class TestLi(unittest.TestCase):
    # Fixture setup method
    def setUp(self):
        self.li = [i for i in range(100)]

    # Fixture teardown method
    def tearDown(self):
        self.li.clear()

    # Test method
    def test_your_list(self):
        self.assertIn(99, self.li)
        self.assertNotIn(100, self.li)

Capital U and capital D

The correct syntax: setUp with capital U and tearDown with capital D.

class TestLi(unittest.TestCase):
  # Fixture setup method
  def setUp(self):
      self.li = [i for i in range(100)]

  # Fixture teardown method
  def tearDown(self):
      self.li.clear()

Example output

The command: python3 -m unittest test_in_list.py

Output of a run with a .setUp() and .tearDown():

output of a run with a fixture

Incorrectly named methods

Output of a run with a .set_up():

output of a run with a fixture with a wrong name

Summary

Fixture in unittest - the preparation needed to perform one or more tests
To create a fixture:
- Implement the .setUp() method
- Implement the .tearDown() method
.setUp() - a method called to prepare the test fixture before the actual test.
.tearDown() - a method called after the test method to clean the environment.

Let's practice!

Introduction to Testing in Python