conftest: set HISTFILE=/dev/null in order not to affect user's history

[akinomyoga]

After running make check or cd test/t; pytest-3 ..., my command histories in ~/.bash_history were washed out. I believe we should set HISTFILE=/dev/null in conftest.py not to affect the users's history.

This time I didn't add the test for this behavior. If you think we need to add tests for tests, please let me know.

Edit: Resolve #321

[akinomyoga]

Now I found an existing issue #321

I vaguely remember that others preferred that a long time ago. But I've always found it very annoying, just haven't got around to it especially now that probably most of my tests are run in dedicated containers. But a clean fix would be very welcome nevertheless. (comment by @scop #321)

I'm not sure what was the purpose of the "others", but if one needs some information on what commands are executed while the tests, how about instead set HISTFILE=./conftest.log so that the commands will be appended to test/fixtures/conftest.log (with conftest.log being added to .gitignore? Of course, we may instead output them in another file outside the git tree, but I'm not sure which place is appropriate for now.

[scop]

Thanks!

[akinomyoga]

Thank you for taking your time to review the PR and fix my English!

[scop]

Forgot to note that I opted to not do anything about a history file of our own for now, let's revisit if there's a case where we'd need that. Loads of output (maybe even too much) can already be obtained by using $BASHCOMP_TEST_LOGFILE.

[akinomyoga]

OK, thank you for the information.

By the way, as for #492, I'm now trying to understand what @pytest.mark.complete does. It seems @pytest.mark.complete cannot be directly used for the present purpose, but maybe I should add another decorator that allows changing the directory and shell settings. I think it takes some time.