Update requirements.txt to include missing packages

[darothen]

When installing via the instructions pip install git+https://github.com/atmos-cloud-sim-uj/PySDM.git in the README from a fresh conda environment w/ Python=3.8, pystrict was not installed so neither the tests nor the demo code could run.

[darothen]

Turns out exdown also was not automatically installed; added.

[codecov-commenter]

Codecov Report

Merging #495 (14e9c52) into master (87eb462) will not change coverage.
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[slayoo]

thanks! (and thank you for the JOSS review!)
I've just removed the pystrict usage from formulae.py - this was the only place the package was used outside of examples, and there seem to be no need for it here: 7130ba0

[slayoo]

Turns out exdown also was not automatically installed; added.

exdown was already here in the requirements, yet I feel that the issue is that we have the requirements split into those listed in setup.py and in requirements.txt. When doing pip install the list from setup.py is used.

Our intention was to use setup.py for the requirements of the code itself, while the requirements.txt file includes packages needed to run tests. The requirements.txt file is used in the CI scripts. Feedback very welcome on how to better address it!

[darothen]

Aha, that makes sense @slayoo. I'm not sure I have a good recommendation off the top of my head other than to keep them synced up manually. Some folks will read in their requirements.txt file in the setup method but that's also kind of finicky. For the sake of the JOSS review, as long as the demo code works out-of-the-box when a user does the recommended installation technique, that's more than fine - the goal is accessibility and ease of use more than anything else, as I understand it.

[slayoo]

One thing that should certainly be improved here is to catch the original problem pointed out by @darothen on CI.

Currently, with Github actions, what we do is as follows:

• install with setup.py (including dependencies: ThrustRTC, CURandRTC, numba, numpy, Pint, chempy, scipy)
• install test-time requirements from requirements.txt(matplotlib, ghapi, pytest, exdown, PySDM-examples)
• run the tests with pytest

The reason to have requirements split across setup.pyand requirements.txt is to cater, e.g., to the users who intend to use PySDM from Matlab or Julia and will not use the examples - real-world case: a Matlab-written parcel model based on PySDM.

The situation caught by @darothen is as follows: we've introduced a new dependency into PySDM code (pystrict) without adding it to the requirements listed in setup.py. However, it was already a dependency of PySDM-examples. So, using PySDM was possible because of installing PySDM-examples, while doing pip install PySDM would actually not give the user a functional instance of PySDM.

So, let's add some hello-world-executing (perhaps even just import) step to CI which will check if using PySDM is possible right after installing it, and before installing other packages.

[slayoo]

here is a PR addressing the above: #496
Let me then close this one.
Thank you @darothen !