If you create a Python file that imports and uses SQLModel, and run it with the Python from your local environment, it will use your cloned local SQLModel source code.
And if you update that local SQLModel source code when you run that Python file again, it will use the fresh version of SQLModel you just edited.
That way, you don't have to "install" your local version to be able to test every change.
"Technical Details"
This only happens when you install using this included requirements.txt instead of running pip install sqlmodel directly.
That is because inside the requirements.txt file, the local version of SQLModel is marked to be installed in "editable" mode, with the -e option.
This command generates a directory ./htmlcov/, if you open the file ./htmlcov/index.html in your browser, you can explore interactively the regions of code that are covered by the tests, and notice if there is any region missing.