test: refactor tmp dir helper fixtures

[Suor]

• tmp_dir descends from Path
• convenient template methods to generate files and dirs, add them to
  dvc and git and commit to git
• independent of old basic_env structures
• can go in any order
• modular: start with empty tmp_dir, initialize git with scm, dvc
  repo with dvc add "repo template" with repo_template, ...

[pared]

Great stuff @Suor. Some minor comments.

Additionaly,
what do you think about removing
repo_template in favor of more granular elements?
For example:

FOO_TEMPLATE = {"foo": "foo"}
@pytest.fixture
def foo(tmp_dir):
    tmp_dir.gen(FOO_TEMPLATE)
    return "foo"

and in test:

def test_add_file(dvc, foo):
    stage, =dvc.add(foo)
    assert os.path.exists(stage.relpath)

also,
using name dvc prevents us from general import dvc. I don't think it should be bloker in any test, as it seems to me that all usages of import dvc are related to patching, and can be replaced with more detailed import. So it is just a comment.

[Suor]

@pared The idea is that helpers will make generating a file so easy that you won't require files precreated with fixtures, which distribute logic over code. In your foo example:

def test_add_file(tmp_dir, dvc):
    stage, = temp_dir.dvc_gen("foo")
    assert os.path.exists(stage.relpath)

So foo fixture saves 0 lines.

[efiop]

Neat!

[Suor]

... (sorry for breaking this)...

This way you may use specific telling names for files, e.g. not reuse code.py as some pregitadded file. Bootstrap specific file structure and play with it in a single place. This should make tests more self-contained and hence more readable.

Getting rid of repo_template might be even better, but it looks like it makes harder to migrate. I also wanted to show it to you, guys. So this remains a design question, do we need to get rid of template?

[Suor]

@MrOutis may you take a look?

[ghost]

really neat; hard to read at the beginning but the interface is awesome 😍
would you mind documenting the intended usage, @Suor? (a quick summary on top of the module is enough))

[Suor]

This is a good idea.

[ghost]

@Suor , what's currently missing from the implementation? (asking because of WIP in title)

[Suor]

@MrOutis It could be merged like this. We will, however, get 3 types of tests this way: unittests, pytest old, pytest new. I thought migrating the rest of the pytes tests first. The thing is the longer this PR lingers here the harder it would be to rebase it. So maybe merging it as is and migrating the rest of the pytest-style tests in a subsequent PR would be easier. What do you think @efiop?

[efiop]

@Suor A bit hesitant because of those reasons, but it is indeed reasonable. Let's do that, but let's also put the converting on the next sprint, so that we don't leave the mess for long. Are you willing to give it shot? 🙂

[Suor]

@efiop I am in.

[efiop]

@Suor Sounds good :)

[Suor]

So, should we merge it? I can add a usage module doc-string in a separate PR.

[efiop]

@Suor At least need to remove WIP suffix, I'm mostly waiting for that.

[Suor]

Done;

[efiop]

@Suor Please create a ticket for the further steps and add it to our sprint, so we can keep track of it.