Loading fixtures in django unit tests

I'm trying to start writing unit tests for django and I'm having some questions about fixtures:

I made a fixture of my whole project db (not certain application) and I want to load it for each test, because it looks like loading only the fixture for certain app won't be enough.

I'd like to have the fixture stored in /proj_folder/fixtures/proj_fixture.json.

I've set the FIXTURE_DIRS = ('/fixtures/',) in my settings.py.
Then in my testcase I'm trying

fixtures = ['proj_fixture.json']
 

but my fixtures don't load.
How can this be solved?
How to add the place for searching fixtures?
In general, is it ok to load the fixture for the whole test_db for each test in each app (if it's quite small)?
Thanks!

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