To check this, do something like this:

$ ./pants dependencies src/python/pants/base: 2>/dev/null | grep 3rdparty/
3rdparty/python:pathspec
3rdparty/python:setproctitle
3rdparty/python:pystache
3rdparty/python:typing-extensions
3rdparty/python:dataclasses
3rdparty/python/twitter/commons:twitter.common.dirutil

Here substitute the targets you pass to test for

src/python/pants/base:

and change the grep to match wherever your requirements.txt / BUILD live.