Jupyter notebooks are a great environment to prototype solutions andexplore their design. Turning these solutions into reusable componentsusually requires moving them out of the notebook environment intoexternal python packages. Often, at this stage, the code is refactoredand test are written.In this talk, I will demo```ipytest`` `__, a small tool to runtests inside notebooks. It supports ```pytest`` `__as well as the standard```unittest`` `__framework. It allows to start prototypes in a notebook and to developthe tests with the code in an highly interactive environment. As thecode grows, it can be transparently moved outside notebooks andtransformed into reusable components. By bringing support for tests tothe notebook environment,```ipytest`` `__ bridges the artificialgap between notebooks and reusable components.