6.2 Some Example Code

Last updated on 2025-05-02 | Edit this page

Estimated time: 10 minutes

Overview

Questions

  • FIXME

Objectives

  • FIXME

Creating a Copy of the Example Code Repository

FIXME: copy factorial-example repo into softwaresaved

For this lesson we’ll need to create a new GitHub repository based on the contents of another repository.

  1. Once logged into GitHub in a web browser, go to https://github.com/UNIVERSE-HPC/ci-example.
  2. Select ‘Use this template’, and then select ‘Create a new repository’ from the dropdown menu.
  3. On the next screen, ensure your personal GitHub account is selected in the Owner field, and fill in Repository name with ci-example.
  4. Ensure the repository is set to Public.
  5. Select Create repository.

You should be presented with the new repository’s main page. Next, we need to clone this repository onto our own machines, using the Bash shell. So firstly open a Bash shell (via Git Bash in Windows or Terminal on a Mac). Then, on the command line, navigate to where you’d like the example code to reside, and use Git to clone it. For example, to clone the repository in our home directory (replacing github-account-name with our own account), and change directory to the repository contents:

BASH 

cd
git clone https://github.com/github-account-name/ci-example
cd ci-example

Examining the Code

Next, let’s take a look at the code, which is in the factorial-example/mymath directory, called factorial.py, so open this file in an editor. You may recall we used this example in the last session on unit testing.

As a reminder, the example code is a basic Python implementation of Factorial. Essentially, it multiplies all the whole numbers from a given number down to 1 e.g. given 3, that’s 3 x 2 x 1 = 6 - so the factorial of 3 is 6.

We can also run this code from within Python to show it working. In the shell, ensure you are in the root directory of the repository, then type:

BASH 

python

PYTHON 

Python 3.10.12 (main, Feb  4 2025, 14:57:36) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

Then at the prompt, import the factorial function from the mymath library and run it:

PYTHON 

>>> from mymath.factorial import factorial
>>> factorial(3)

Which gives us 6 - which gives us some evidence that this function is working. But this isn’t really enough evidence to give us confidence in its overall correctness.

Running the Tests

For this reason, this code repository already has a series of unit tests, that allows us to automate this results checking, written using a Python unit testing framework called pytest. Note that this is a different unit testing framework that we looked at in the last session!

Navigate to the repository’s tests directory, and open a file called test_factorial.py:

PYTHON 

import pytest
from mymath.factorial import factorial


def test_3():
    assert factorial(3) == 6

def test_5():
    assert factorial(5) == 120

def test_negative():
    with pytest.raises(ValueError):
      factorial(-1)

The key difference when writing tests for pytest as opposed to unittest, is that we don’t need to worry about wrapping the tests in a class: we only need to write functions for each test, which is a bit simpler. But they otherwise essentially work very similarly in both frameworks.

So essentially, this series of tests will check whether calling our factorial function gives us the correct result, given a variety of inputs:

  • factorial(3) should give us 6
  • factorial(5) should give us 120
  • factorial(-1) should raise a Python ValueError which we need to check for

Setting up a Virtual Environment for pytest

So how do we run these tests? Well, we need to create a virtual environment, since we’re using a unit test framework that’s supplied by another Python library which we need to have access to.

You may remember we used virtual environments previously. So in summary, we need to:

  • Create a new virtual environment to hold packages
  • Activate that new virtual environment
  • Install pytest into our new virtual environment

So:

BASH 

python -m venv venv

Then to activate it:

BASH 

[Linux] source venv/bin/activate
[Mac] source venv/bin/activate
[Windows] source venv/Scripts/activate

To install pytest:

BASH 

pip install pytest

Then, in the shell, we can run these tests by ensuring we’re in the repository’s root directory, and running the following (very similar to how we ran our previous unittest tests):

BASH 

python -m pytest tests/test_factorial.py

You’ll note the output is slightly different:

OUTPUT 

============================= test session starts ==============================
platform linux -- Python 3.10.12, pytest-8.3.5, pluggy-1.5.0
rootdir: /home/steve/test/ci-example2
collected 3 items

tests/test_factorial.py ...                                              [100%]

============================== 3 passed in 0.00s ===============================

But essentially, we receive the same information: a . if the test is successful, and a F if there is a failure.

We can also ask for verbose output, which shows us the results for each test separately, in the same way as we did with unittest, using the -v flag:

BASH 

python -m pytest -v tests/test_factorial.py

OUTPUT 

============================= test session starts ==============================
platform linux -- Python 3.10.12, pytest-8.3.5, pluggy-1.5.0 -- /home/steve/test/ci-example2/venv/bin/python
cachedir: .pytest_cache
rootdir: /home/steve/test/ci-example2
collected 3 items

tests/test_factorial.py::test_3 PASSED                                   [ 33%]
tests/test_factorial.py::test_5 PASSED                                   [ 66%]
tests/test_factorial.py::test_negative PASSED                            [100%]

============================== 3 passed in 0.00s ===============================

[CHECKPOINT - who’s run the tests and got this output? Yes/No]

Key Points

  • FIXME