What is the difference between setUp() and setUpCl

Question

What is the difference between setUp() and setUpClass() in the Python unittest framework? Why would setup be handled in one method over the other?

I want to understand what part of setup is done in the setUp() and setUpClass() functions, as well as with tearDown() and tearDownClass().

Answer 1

The difference manifests itself when you have more than one test method in your class. setUpClass and tearDownClass are run once for the whole class; setUp and tearDown are run before and after each test method.

For example:

class Example(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        print("setUpClass")

    def setUp(self):
        print("setUp")

    def test1(self):
        print("test1")

    def test2(self):
        print("test2")

    def tearDown(self):
        print("tearDown")

    @classmethod
    def tearDownClass(cls):
        print("tearDownClass")

When you run this test, it prints:

setUpClass
setUp
test1
tearDown
.setUp
test2
tearDown
.tearDownClass

(The dots (.) are unittest's default output when a test passes.) Observe that setUp and tearDown appear before and after test1 and test2 respectively, whereas setUpClass and tearDownClass appear only once, at the beginning and end of the whole test case.

Answer 2

After reading both question and the accepted answer, I think some supplement can be made.

Q: Why would setup be handled in one method over the other?
A: It's because the test method may need preliminary and the preliminary varies from test method to test method.

For example, take below code from https://www.tutorialspoint.com/unittest_framework/unittest_framework_api.htm as a sample:

import unittest

class simpleTest2(unittest.TestCase):
   def setUp(self):
      self.a = 10
      self.b = 20
      name = self.shortDescription()
      if name == "add":
         self.a = 10
         self.b = 20
         print name, self.a, self.b
      if name == "sub":
         self.a = 50
         self.b = 60
         print name, self.a, self.b
   def tearDown(self):
      print '\nend of test',self.shortDescription()

   def testadd(self):
      """add"""
      result = self.a+self.b
      self.assertTrue(result == 30)
   def testsub(self):
      """sub"""
      result = self.a-self.b
      self.assertTrue(result == -10)

if __name__ == '__main__':
   unittest.main()

The method testadd and testsub needs different input and we can set the value of the input respectively in setUp method.