Ensure compatibility with xdist

[esafak]

This plugin does not appear to co-operate with the xdist distributed testing plugin. Can this be overcome?

[ftobia]

Do you mean that test order isn't preserved if you run your tests with multiple CPUs? I think that this limitation could be overcome in theory, though I'm not sure how valuable that solution would be, since synchronizing the tests would seem to be at odds with parallelizing them. I suppose there could be a way of determining which tests depend on others, and running them in a single thread, and parallelizing the other tests.

[esafak]

You do not need to determine anything; the user already marks up the dependency graph through decorators. The problem is merely ensuring dependent tests are executed serially in the same thread.

Suppose I have a bunch of tests but a subset of them have dependencies. Parallelization would still yield benefits.

[andyg0808]

Just to note: I think the ordering is preserved, but the tests end up run in different processes when there's more than one. I'm using pytest-ordering to ensure the slowest tests are started first, and it works nicely for that.

The xdist plugin seems to schedule tests as it wishes. But if we use the --dist=loadfile option, we can ask xdist to schedule all the tests from one file on the same thread. So if each group of dependent tests can be put in one file, we can make sure that the tests from each file get run on the same thread, and it appears pytest-ordering will correctly sort the tests per-file under those conditions. See #52 for a test to demonstrate this.

[uniqueni]

i am facing this issue
when i use pytest-xdist and pytest-ordering
error occurred