run tests in parallel

[smark-1]

when I run docker compose exec -w /code/wagtail web python runtests.py --parallel the tests run significantly faster then when I run docker compose exec -w /code/wagtail web python runtests.py without --parallel.

CPU, Memory, and Disk usage appear to be approximately the same. So adding this to the make file would be a big win for me.

[laymonage]

We should probably add a separate command for this (or make it possible to pass additional arguments to make test to be passed on to runtests.py). Running tests in parallel is definitely much faster, but sometimes Django/unittest cannot produce a helpful traceback due to some pickling issues, in which case you'd still want to run it in serial.

[saevarom]

We could perhaps just add a separate command that runs in parallel for time being? E.g. have both make test and make test-parallel in the Makefile. @smark-1 could you change the PR so that we have these two commands?

Unless @laymonage has a goto solution for passing arguments from the make command, which to me seems like a slightly bigger task.

[laymonage]

I don't have the solution and yep it is quite a task in itself, so I just put it in parentheses in case we do want to figure that one out 😆

But yes, I'm happy with just a separate command!

[smark-1]

@saevarom I updated the PR. I am not sure what the best way to document this is.

1. test-parallel be a new subsection in the docs?
2. Or should be mentioned as an comment above each make test ... option?
3. Or a paragraph somewhere saying your can replace make test with make test-parallel to run faster but it sometimes cannot produce a helpful traceback?
4. other?