Python Unit Testing

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Unit Testing

For unit testing, the code to test shall be separated in a own class. The class will be written in a file, which can be executed for the unit tests. For the tests, simply every class gets a test class, which is derived from unittest.TestCase. All methods there which start with test_ will be executed as test.

import unittest

class TextFormatter:
	def __init__(self, upperCase=False):
		self.upperCase = upperCase

	def do_format(self, text):
		return text.lower()


class Test_TextFormatter(unittest.TestCase):
	def setUp(self):
		pass;

	def test_do_format_lowercase(self):
		formatter = TextFormatter(False)
		self.assertEqual(formatter.do_format("Abc"), "abc")

	def test_do_format_uppercase(self):
		formatter = TextFormatter(True)
		self.assertEqual(formatter.do_format("Abc"), "ABC")

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

The output is straight forward:

$ python3 formatter.py
.F
======================================================================
FAIL: test_do_format_uppercase (__main__.Test_TextFormatter)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/charly/Projects/python_test/formatter.py", line 21, in test_do_format_uppercase
    self.assertEqual(formatter.do_format("Abc"), "ABC")
AssertionError: 'abc' != 'ABC'
- abc
+ ABC


----------------------------------------------------------------------
Ran 2 tests in 0.001s

FAILED (failures=1)
$

Source: python.org

Mocking

With mocking there are two ways to go:

MagicMock: The MagicMock can be used to replace object and methods. Objects can be filled with parameters and methods. Methods can be set a return value and it's use (call count, etc) can be evaluated.
mock.patch: With mock.patch normal and static methods can be replaced.

from unittest.mock import MagicMock
import mock

class Test_Connection(unittest.TestCase):
    def setUp(self):
        self.__testDevice = MagicMock()
        self.__testDevice.query_str = MagicMock()
        self.__testDevice.query_str.return_value = "0, no Error"
        self.__testDevice.write_str = MagicMock()
        self.__testDevice.open = MagicMock()
        self.__testDevice.close = MagicMock()

    @mock.patch.object(RsInstrumentConnection, '_create_connection')
    def test_write(self, create_connection_mock):
        create_connection_mock.return_value = self.__testDevice
        with RsInstrumentConnection("TestDevice") as visa:
            visa.write("TestCommand")
            create_connection_mock.assert_called_once_with('TCPIP::TESTDEVICE::HISLIP0')
            self.__testDevice.write_str.assume_called_once_with("TestCommand") # pylint: disable=no-member
        self.__testDevice.close.assume_called_once()