How to supply a mock class method for python unit test?

Question

Let\'s say I have a class like this.

   class SomeProductionProcess(CustomCachedSingleTon):

       def loaddata():
           \"\"\"
           Uses an iterator         


        

Answer 1

Lets say you have a module named awesome.py and in it, you had:

import time

class SomeProductionProcess(CustomCachedSingleTon):

    def loaddata(self):
        time.sleep(30) # simulating a long running process
        return 2

Then your unittest where you mock loaddata could look like this:

import unittest

import awesome # your application module


class TestSomeProductionProcess(unittest.TestCase):
    """Example of direct monkey patching"""

    def test_loaddata(self):
        some_prod_proc = awesome.SomeProductionProcess()
        some_prod_proc.loaddata = lambda x: 2 # will return 2 every time called
        output = some_prod_proc.loaddata()
        expected = 2

        self.assertEqual(output, expected)

Or it could look like this:

import unittest
from mock import patch

import awesome # your application module

class TestSomeProductionProcess(unittest.TestCase):
    """Example of using the mock.patch function"""

    @patch.object(awesome.SomeProductionProcess, 'loaddata')
    def test_loaddata(self, fake_loaddata):
        fake_loaddata.return_value = 2
        some_prod_proc = awesome.SomeProductionProcess()

        output = some_prod_proc.loaddata()
        expected = 2

        self.assertEqual(output, expected)

Now when you run your test, loaddata wont take 30 seconds for those test cases.