testdriven.io: Test-Driven Development with FastAPI and Docker: Why do we pull an image, build it again and test it instead of just testing directly?

Question

Taken from the tutorial we see the following:

In the build job, we:

1. Check out the repository so the job has access to it
2. Log in to GitHub Packages
3. Pull the image if it exists
4. Build the image
5. Push the image up to GitHub Packages

The same steps are done for the test job. My question is what purpose or benefit do we have from building the image again if we already built it using the same code in the previous step. Imho pulling the image accomplishes nothing for this job. Or am I missing something?