Add expecttest to requirements.txt (#63320)
Summary:
This PR closes the developer environment gap left by https://github.com/pytorch/pytorch/issues/60658 by adding [expecttest](https://github.com/ezyang/expecttest) to `requirements.txt`. Thus it provides a solution to one of the short-term problems that https://github.com/pytorch/pytorch/issues/60697 tries to solve, but does not provide a long-term solution to https://github.com/pytorch/pytorch/issues/61375.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63320
Reviewed By: malfet
Differential Revision: D30340654
Pulled By: samestep
fbshipit-source-id: 26c8f8c9889cce4a94fafb1bf2f0d6df4c70503f
