Chaining tests and passing an object from one test to another

For sharing data between tests, you could use the pytest namespace or cache.

Namespace

Example with sharing data via namespace. Declare the shared variable via hook in conftest.py:

# conftest.py

import pytest


def pytest_namespace():
    return {'shared': None}

Now access and redefine it in tests:

import pytest


def test_creation():
    pytest.shared = 'spam'
    assert True


def test_deletion():
    assert pytest.shared == 'spam'

Cache

The cache is a neat feature because it is persisted on disk between test runs, so usually it comes handy when reusing results of some long-running tasks to save time on repeated test runs, but you can also use it for sharing data between tests. The cache object is available via config. You can access it i.e. via request fixture:

def test_creation(request):
    request.config.cache.set('shared', 'spam')
    assert True


def test_deletion(request):
    assert request.config.cache.get('shared', None) == 'spam'

ideally this test should only run if the previous test was successful

There is a plugin for that: pytest-dependency. Example:

import pytest


@pytest.mark.dependency()
def test_creation():
    assert False


@pytest.mark.dependency(depends=['test_creation'])
def test_deletion():
    assert True

will yield:

$ pytest -v
============================= test session starts =============================
...
collected 2 items

test_spam.py::test_creation FAILED                                      [ 50%]
test_spam.py::test_deletion SKIPPED                                     [100%]

================================== FAILURES ===================================
________________________________ test_creation ________________________________

    def test_creation():
>       assert False
E       assert False

test_spam.py:5: AssertionError
===================== 1 failed, 1 skipped in 0.09 seconds =====================