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Github actions

Core Module

With the tests established in the previous module we are now ready to move on to actually implementing some continuous integration in our pipeline. As you probably have already realized testing your code locally may take cumbersome to do, because

  • You need to run it often to make sure to catch bugs early on
  • If you want to have high code coverage of your code base, you will need many tests that takes a long time to run

For these reasons we want to automate the testing, such that it done every time we push to our repository. If we combine this with only pushing to branches and then only merging these branches whenever all automated testing have passed, our code should be fairly safe against unwanted bugs (assuming your tests are well covering your code).

Github actions

Github actions are the CI solution that Github provides. Each of your repositories gets 2,000 minutes of free testing per month which should be more than enough for the scope of this course (and probably all personal projects you do). Getting Github actions setup in a repository may seem complicated at first, but workflow files that you create for one repository can more or less be reused for any other repository that you have.

Lets take a look at how a github workflow file is organized:

  • Initially we start by giving the workflow a name
  • Next we specify on what events the workflow should be triggered. This includes both the action (pull request, push etc) and on what branches is should activate
  • Next we list the jobs that we want to do. Jobs are by default executed in parallel but can also be dependent on each other
  • In the runs-on we can specify which operation system we want the workflow to run on. We also have the possibility to specify multiple.
  • Finally we have the steps. This is where we specify the actual commands that should be run when the workflow is executed.


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❔ Exercises

  1. Start by creating a .github folder in the root of your repository. Add a sub-folder to that called workflows.

  2. Go over this page that explains how to do automated testing of python code in github actions. You do not have to understand everything, but at least get a feeling of what a workflow file should look like.

  3. We have provided a workflow file called tests.yml that should run your tests for you. Place this file in the .github/workflows/ folder. The workflow file consist of three steps

    • First a python environment is setup (in this case python 3.8)

    • Next all dependencies required to run the test are installed

    • Finally, pytest is called and test will be run

  4. For the script to work you need to define the requirements.txt and requirements_tests.txt. The first file should contain all packages required to run your code. The second file is all additional packages required to run the tests. In your simple case it may very well be that the second file is empty, however sometimes additional packages are used for testing that are not strictly required for the scripts to run.

  5. Finally, try pushing the changes to your repository. Hopefully your tests should just start, and you will after sometime see a green check mark next to hash of the commit. Also try to checkout the Actions tap where you can see the history of actions run.


  6. Normally we develop code one operating system and just hope that it will work on other operating systems. However, CI enables us to automatically test on other systems than ourself.

    1. The provided tests.yml only runs on one operating system. Which one?

    2. Alter the file (or write a new) that executes the test on the two other main operating systems that exist.

  7. As the workflow is currently setup, github actions will destroy every downloaded package when the workflow has been executed. To improve this we can take advantage of caching:

    1. Figure out how to implement caching in your workflow file. You can find a guide here and here.

    2. When you have implemented a caching system go to Actions->Caches in your repository and make sure that they are correctly added. It should look something like the image below


    3. Measure how long your workflow takes before and after adding caching to your workflow. Did it improve the runtime of your workflow?

  8. (Optional) Code coverage can also be added to the workflow file by uploading it as an artifact after running the coverage. Follow the instructions in this post on how to do it.

  9. As stated in the introduction, ideally we want to only push our code to branches, such that our workflows run before we actually merge code into our codebase. We can directly prevent bad behavior by adding branch protection rules to our repository. Take the image below as an example from one of my own PRs:


    In this example, the PR cannot be merge to the main branch before the following is fulfilled: At least 2 reviewers with write access have approved the PR, all Github actions marked as Required are passing and all conversations needs to be resolved. Since not all important tests are passing, further changes are necessary. We want to implement something similar. Do the following:

    1. On your Github repository of choice, go to Settings -> Branches -> Add branch protection rule:

    2. To your main/master branch add the following rules:

      • At least one person needs to approve any PR
      • All your workflows has to pass
      • All conversations needs to be resolved
    3. To test that everything works, try creating a PR (possibly with a small bug) and see that your main/master branch is protected

  10. One problem you may have encountered is running your tests that have to do with your data, with the core problem being that your data is actually not stored in github (assuming you have done module M8 - DVC) and therefore cannot be tested. However, it is possible for us to download data while running our CI. Lets try to setup that:

    1. The first problem is that we need our CI needs to be able to authenticate with the our storage solution. We can take advantage of an authentication file that is created the first time we push with DVC. It is located in $CACHE_HOME/pydrive2fs/{gdrive_client_id}/default.json where $CACHE_HOME depends on your operating system:


      This is the typical location, but it may vary depending on what distro you are running


      Find the file. The content should look similar to this (only some fields are shown):

          "access_token": ...,
          "client_id": ...,
          "client_secret": ...,
          "refresh_token": ...,
    2. The content of that file is should be treated as an password an not shared with the world and the relevant question is therefore how to use this info in public repository. The answer is github secrets, where we can store information, access it in our workflow files and it is still not public. Navigate to the secrets option (as shown below) and create a secret with the name GDRIVE_CREDENTIALS_DATA that contains the content of the file you found in the previous exercise.


    3. Afterwards, add the following code to your workflow file:

      - uses: iterative/setup-dvc@v1
      - name: Get data
        run: dvc pull

      that runs dvc pull using the secret authentication file. For help you can visit this small repository that implements the same workflow.

    4. Finally, add the changes, commit, push and confirm that everything works as expected. You should now be able to run unit tests that depends on your input data.

  11. In module M6 on good coding practices (optional module) of the course you where introduced to a couple of good coding practices such as being consistent with your coding style, how your Python packages are sorted and that your code follows certain standards. All this was done using the ruff framework. In this set of exercises we will setup github workflows that will automatically test for this.

    1. Create a new workflow file called codecheck.yml, that implements the following three steps

      • Setup python environment

      • Installs ruff

      • Runs ruff check and ruff format on the repository

      (HINT: You should be able to just change the last steps of the tests.yml workflow file)

    2. In addition to ruff we also used mypy in those set of exercies for checking if the typing we added to our code was good enough. Add another step to the codecheck.yml file which runs mypy on your repository.

    3. Try to make sure that all steps are passing on repository. Especially mypy can be hard to get passing, so this exercise formally only requires you to get ruff passing.

🧠 Knowledge check

  1. When working with Github actions you will often encounter the following 4 concepts:

    • Workflow
    • Runner
    • Job
    • Action

    Try to define them with your own words.

    • Workflow: A yaml file that defines the instructions to execute on specific events. Needs to be placed in the .github/workflows folder.
    • Runner: Workflows need to run somewhere. The environment that the workflow is being executed on is called the runner. Most commonly the runner is hosted by Github but can also hosted by yourself.
    • Job: A series of steps which are executed on the same runner. A workflow must include at least one job, but often contains many.
    • Action: A action is the smallest unit in a workflow. Jobs often consist of multiple actions that are executed sequentially.
  2. The on attribute specify upon which events the workflow will be triggered. Assume you have set the on attribute to the following:

          branches: [main]
          branches: [main]
          - cron: "0 0 * * *"
        workflow_dispatch: {}

    What 4 events would trigger the execution of that action?

    1. Direct push to branch main would trigger it
    2. Any pull request opened that will merge into main would trigger it
    3. At the end of the day the action would trigger
    4. The trigger can be executed by manually triggering it through the Github UI, example shown below


This ends the module on Github workflows. If you are more interested in this topic you can checkout module M31 on documentation which first including locally building some documentation for your project and afterwards use Github actions for deploying it to Github Pages. Additionally, Github also have a lot of templates already for running a lot CI tasks. If you try to create a workflow file directly in Github you may encounter the following page


We highly recommend checking this out if you want to write any other kind of CI pipeline in Github actions. We can also recommend this repository that have an list of awesome actions and checkout the act repository which is a tool for running your GitHub Actions locally!