Move isort/lint commands out of test runner

[rpkilby]

In general, it doesn't seem necessary to integrate linting and sorting into the test runner. This method complicates running isort with specific options, such as --diff. Moving the command into tox simplifies this, and options can be provided after the -- options separator. eg,

$ tox -e isort -- --diff

Note that the lint travis build runs both the isort and lint builds.

[rpkilby]

I don't know if anyone is particularly attached to running isort/flake8 through the test runner.

[blueyed]

Makes sense.
In the long run we should get completely rid of runtests.py.

[xordoquy]

In the long run we should get completely rid of runtests.py.

We have had this talk before and @tomchristie said no. Can't remember the argument though.

I don't know if anyone is particularly attached to running isort/flake8 through the test runner.

Yes I am. Removing it seems a good way to just discard it simply.

[carltongibson]

TBH I don't really see the point of this change (or the problem with runtests.py).

Let me close this for now. But I'm happy to discuss it a bit here so we can air the pros and cons. It's easy enough to re-open. (OK?)

[blueyed]

I really like this change, since it removes an unnecessary wrapper (the custom runtests.py).
It is easier to run it through tox, which has a well-known interface.

@xordoquy

Removing it seems a good way to just discard it simply.

Do you mean that isort gets not checked then anymore?
There would be flake8-isort which could be used (so that it's done with the flake8 run), and runtests.py could be changed (in this PR) to still run isort via the new tox env, possibly through flake8-isort then.

[rpkilby]

The intent was to fix a minor annoyance with running isort. The test runner doesn't pass command line arguments to isort, so if you want to use --diff or other options, you either need to invoke isort directly and remember the appropriate arguments, or temporarily modify runtests.py to include those options.

Alternatively, We could add the --diff argument to the test runner, but $ tox -e isort -- --diff seems a little cleaner. Then again, I don't usually invoke the test runner directly and prefer to run the tests via tox, so I'm predisposed to the latter. Again, a small change to fix to a minor annoyance - I don't have particularly strong opinions on this.