Why would you want to update requirements.txt before testing against the new package version first?<p>My dependency upgrade workflow for a Python web app is usually:<p><pre><code>    run pip list --outdated
    upgrade one package
    run tests
        if success
            pip freeze to update this package (and its dependencies)
            commit
        else
            investigate or revert and make a note for later (if many breaking changes, etc.)
</code></pre>
Perhaps this could be useful if you&#x27;re using tox to test against many versions of Python, e.g. for a library.<p>(Or if you only freeze top-level dependencies, even though that goes against best practices.)