Make test suite more efficient to run in 10 minutes

Description of the desired feature

PyGMT’s test suite is growing, and in the long-term, we’ll need to make testing a bit more efficient for contributors. As a goal, we should aim for ~10 minutes for the whole test suite (Windows takes up ~~30min~ 15min now (see #586)), and <1 minute for local tests on just one module.

Here’s a few ways we can tackle this (note to maintainers, feel free to edit this top post):

Local tests

Running make test can be slow since it runs everything, but sometimes we only want to test one function (e.g. grdimage).

• E.g. at https://github.com/GenericMappingTools/pygmt/pull/516#discussion_r464184518, we should document that contributors can run just one test using something like pytest -v --mpl pygmt/tests/test_grdimage.py.
• Alternatively, look into something like pytest-fastest to automate testing only the code that has changed between the current branch and master.

Github Actions tests

Installing dependencies

The bulk of the CI time is spent installing dependencies from conda (4min on Linux, 9min on Windows). We could:

• Cache dependencies. This was experimented before, but it didn’t seem to help (see https://github.com/GenericMappingTools/pygmt/pull/475#issuecomment-656392670), could try again to see things have changed
• Try switching to mamba which is a fast reimplementation of conda written in C++. I’ve tried it before, but it’s still in experimental mode at setup-miniconda, see https://github.com/conda-incubator/setup-miniconda#example-6-mamba (#841)

Speed up full test suite

Find a way to run a minimal set of tests when Pull Request is in draft, and only full test suite when Pull Request is ready to review/in review?

Are you willing to help implement and maintain this feature? Let’s do it together 😄

[willschlitzer]

It works! Thanks @weiji14!

[weiji14]

You also need to add your ssh key to your GitHub account https://docs.github.com/en/github/authenticating-to-github/adding-a-new-ssh-key-to-your-github-account.