TIL how to re-run only failed tests

Fri, 21 Nov 2025 13:00:00 +0000

This is a super small thing I stumbled over. When I implement a new feature, there is inevitably a step where I go through the failing pytest tests and fix or clarify them.

Unless I use an IDE, my work loop is like this:

Make code change
Run python -m pytest
Check which tests are failing.
Go back to 1.

Now, 2. runs all tests which can take quite some time. There is always the option to run a specific test only, but multiple failing tests can be scattered across different files.

Clearing up confusion around IPython, ipykernel, and Jupyter notebooks

Mon, 26 Aug 2024 00:00:00 +0000

One of my big recurring time sinks while doing data science work used to be trying to get my colleagues’ jupyter notebooks to run on my machine. The main contributing factors:

My team generally uses poetry environments to improve reproducibility, but sometimes dependencies aren’t specified
I use VS code and the jupyter extension to edit notebooks in VS code which requires more configuration then running the Jupyter web UI.
I lacked a clear understanding of the differences of IPython, ipykernel, jupyter and which python environments are being used when running a notebook.

So this is my attempt at a friendcatcher . I hope this saves you a few minutes the next time you run into similar issues.

Python on staticnotes.org

TIL how to re-run only failed tests

Clearing up confusion around IPython, ipykernel, and Jupyter notebooks