unittest_examples.py

import pytest
from unittest.mock import Mock
import os

### Some Examples, how to write test functions ###


###### Simple Test ######
def f1():               #function to test
    return 3

def test_f1():          #test function
    assert f1() == 3
#########################


##### Parameterization #####
# Usage: call the test-function several times with different parameters
def f2(x):
    return x+1

@pytest.mark.parametrize(
"input,expected",
[(1,2),
(5,6),
(8,9)])
def test_f2(input, expected):
    assert f2(input) == expected
###########################


##### Test Exceptions #####
# Usage: The function to test returns an exception
def f3():
    raise SystemExit(1)

def test_f3():
    with pytest.raises(SystemExit):
        f3()
###########################


##### Mocking Objects #####
# Usage: the function to test needs complex arguments.
# These arguments can be mocked via Mock-objects.
# Note: More complex examples can be found in error_estimator_test.py (using MagicMock to mock an oject of Main)
def f4(reference):
    return reference.get_result()

def test_f4():
    mock_ref = Mock()
    mock_ref.get_result.return_value = 'xyz'
    actual = f4(mock_ref)

    assert actual == 'xyz'
###########################


##### Monkey-Patching #####
# Usage: The function to test calls functions of an outside module, uses environmental variables,...
# Monkey-Patching substitutes the behavior/variable with a predefined value
def f5():
    return os.getcwd()      #returns current working directory (very specific for each computer) -> monkey-patch it

def test_f5(monkeypatch):
    def monkey_return():    #function which shall be called instead of os.getcwd()
        return 'home/name/'

    monkeypatch.setattr(os, 'getcwd', monkey_return)    #choose module and function which shall be substituted
    assert f5() == 'home/name/'
############################

##### Fixture #####
# Usage: Multiple usages (see documentation); one use case is to execute an expensive calculation once and use it in several tests
# Note: aggregrator_test.py shows an example of a fixture (the instance of Aggregator is a fixture in some tests)
# Beware: If the fixture is an instance of a class, it can happen that "changing the fixture" in one test, can influence another test.
# That is not the case here
@pytest.fixture(scope="module") #calc fixture once per module
def calc():
    return True                 #here, we could have a creation of an instance of some class -> this instance can be used in several tests

def test(calc):                 #the fixture is given to the test-function
    assert calc == True         #here, we could call functions for this class and assert their value,...
    calc = False

def test2(calc):
    assert calc == True
###################