Fix handling of duplicate args with regard to Python packages

[blueyed]

Packages are collected twice.

Fails with:

E       Failed: nomatch: 'collected 2 items'
E           and: '==================================================================================== test session starts ====================================================================================='
E           and: 'platform linux -- Python 3.6.6, pytest-3.10.1.dev18+g01c8fab1, py-1.7.0, pluggy-0.8.0'
E           and: "hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('…/Vcs/pytest/.hypothesis/examples')"
E           and: 'rootdir: /tmp/pytest-of-user/pytest-683/test_collect_init_tests0, inifile: pytest.ini'
E           and: 'plugins: testmon-0.9.13, hypothesis-3.71.10'
E       exact match: 'collected 2 items'
E       fnmatch: '<Package *'
E          with: "<Package '/tmp/pytest-of-user/pytest-683/test_collect_init_tests0/tests'>"
E       nomatch: "  <Module '__init__.py'>"
E           and: "  <Package '/tmp/pytest-of-user/pytest-683/test_collect_init_tests0/tests'>"
E           and: "    <Module '__init__.py'>"
E           and: "      <Function 'test_init'>"
E           and: "    <Module 'test_foo.py'>"
E           and: "      <Function 'test_foo'>"
E           and: ''
E           and: '================================================================================ no tests ran in 0.02 seconds ================================================================================'
E           and: ''
E       remains unmatched: "  <Module '__init__.py'>"

…/Vcs/pytest/testing/test_collection.py:970: Failed

Found while looking into #4310.

[blueyed]

Found a fix.
I still think collection needs some cleanup (#4310 (comment)).

This was introduced with e041823, but before it would only collect 1 item:

collected 1 item
<Package '/tmp/pytest-of-daniel/pytest-760/test_collect_init_tests0/tests'>
  <Module 'test_foo.py'>
    <Function 'test_foo'>

[blueyed]

Sorry, it does not fix #4310 yet.

[blueyed]

Reverted _collect_seen_pkgdirs which was meant to collect packages first, but test_generate_tests_only_done_in_subdir failed with it.
This now documents the current behavior, where we get the same package twice for example, but it should not have duplicates anymore.

[nicoddemus]

Definitely agree that we need to improve collection tests coverage and refactor the code itself.

[blueyed]

Ahem.. this was not really ready for merging - there is e.g. a TODO commit in there.. :/

Sorry for not marking it WIP, but it is clearly visible from the commit history..

[RonnyPfannschmidt]

ouch my bad, i did read the commit lines but i completely missed the TODO:

[blueyed]

..and the XXX.

Typically I would like to get fixes / refactors like this into a single commit (not even the annoying merge commits), i.e. squash-merge them when ready.

It is really frustrating to go back and forth with all the single commits that have been done in this area already for the package-scoped fixtures.. :(

[blueyed]

..and everything in this regard seems to be ad-hoc, instead of discussing/reviewing stuff carefully.

[blueyed]

btw: can black be told to keep these as separate lines?
It is much more readable then IMHO.

[RonnyPfannschmidt]

@blueyed you can use # fmt: off/on blocks for those, i believe we also support multiline strings that will be split/striped

[nicoddemus]

AFAIK black doesn't have many configuration options, on purpose.