test_functions

test_functions_w_pass

red: make it fail

  • I open a terminal to run makePythonTdd.sh with functions as the name of the project

    ./makePythonTdd.sh functions

    on Windows without Windows Subsystem Linux use makePythonTdd.ps1

    ./makePythonTdd.ps1 functions

    it makes the folders and files that are needed, installs packages, runs the first test, and the terminal shows AssertionError

    E       AssertionError: True is not false

tests/test_functions.py:7: AssertionError

  • I hold ctrl (windows/linux) or option (mac) on the keyboard and use the mouse to click on tests/test_functions.py:7 to open it in the editor

  • then change True to False

  • and change test_failure

import unittest
import functions


class TestFunctions(unittest.TestCase):

    def test_functions_w_pass(self):
        self.assertIsNone(functions.function_w_pass())

the terminal shows ModuleNotFoundError , and I add it to the list of Exceptions encountered

# Exceptions Encountered
# AssertionError
# ModuleNotFoundError

green: make it pass

  • I make a file called functions.py in the project folder and the terminal shows AttributeError, which I add to the list of Exceptions encountered

    # Exceptions Encountered
# AssertionError
# ModuleNotFoundError
# AttributeError

  • I add a function definition to functions.py

    def function_w_pass():
    pass

    and we have a passing test

    • the test checks if the value of the call to functions.function_w_pass is None

    • the function definition simply says pass yet the test passes

    • pass is a placeholder keyword which allows the function definition to follow Python syntax rules

    • the test passes because in Python all functions return None by default, like the function has an invisible line that says return None

test_functions_w_return

red: make it fail

I add a new failing test to TestFunctions in test_functions.py to check that functions always return None

def test_functions_w_return(self):
    self.assertIsNone(functions.function_w_return())

the terminal shows AttributeError

green: make it fail

I add a new function to functions.py to make the test pass, this time with a return statement instead of pass

def function_w_return(self):
    return

the terminal shows this test also passes

I defined 2 functions with different statements in their body but they both return the same result, because “in Python all functions return None by default, like the function has an invisible line that says return None”

test_functions_w_return_none

red: make it fail

I add one more test to the TestFunctions class in test_functions.py to help drive home the point

def test_functions_w_return_none(self):
    self.assertIsNone(
        functions.function_w_return_none()
    )

the terminal shows AttributeError

green: make it pass

from the Zen of Python: Explicit is better than implicit. I add a function definition to functions.py this time with an explicit return statement showing the value returned

def function_w_return_none():
    return None

and the terminal shows passing tests.

review

The 3 ways I have defined functions so far have the exact same outcome, they all return None. If Explicit is better than implicit. then I prefer to use return None telling anyone who reads the code exactly what the function returns.

Here is what I know so far from the tests

Would you like to test singleton functions?

functions: tests and solutions