Do not call django.setup() multiple times (#629)

Fixes #531.

Author: blueyed

docs/conf.py

@@ -44,4 +44,15 @@
     'python': ('https://docs.python.org/3', None),
     'django': ('https://docs.djangoproject.com/en/dev/',
                'https://docs.djangoproject.com/en/dev/_objects/'),
+    'pytest': ('https://docs.pytest.org/en/latest/', None),
 }
+
+
+def setup(app):
+    # Allow linking to pytest's confvals.
+    app.add_description_unit(
+        "confval",
+        "pytest-confval",
+        objname="configuration value",
+        indextemplate="pair: %s; configuration value",
+    )

docs/configuring_django.rst

@@ -83,3 +83,22 @@ This can be done from your project's ``conftest.py`` file::
     def pytest_configure():
         settings.configure(DATABASES=...)
 
+Changing your app before Django gets set up
+-------------------------------------------
+
+pytest-django calls :py:func:`django.setup` automatically.  If you want to do
+anything before this, you have to create a pytest plugin and use
+the :py:func:`~_pytest.hookspec.pytest_load_initial_conftests` hook, with
+``tryfirst=True``, so that it gets run before the hook in pytest-django
+itself::
+
+    @pytest.hookimpl(tryfirst=True)
+    def pytest_load_initial_conftests(early_config, parser, args):
+        import project.app.signals
+
+        def noop(*args, **kwargs):
+            pass
+
+        project.app.signals.something = noop
+
+This plugin can then be used e.g. via ``-p`` in :pytest-confval:`addopts`.

pytest_django/plugin.py

@@ -150,7 +150,10 @@ def _setup_django():
     if not django.conf.settings.configured:
         return
 
-    django.setup()
+    import django.apps
+    if not django.apps.apps.ready:
+        django.setup()
+
     _blocking_manager.block()
 
 

tests/test_initialization.py

@@ -0,0 +1,50 @@
+from textwrap import dedent
+
+
+def test_django_setup_order_and_uniqueness(django_testdir, monkeypatch):
+    """
+    The django.setup() function shall not be called multiple times by
+    pytest-django, since it resets logging conf each time.
+    """
+    django_testdir.makeconftest('''
+        import django.apps
+        assert django.apps.apps.ready
+        from tpkg.app.models import Item
+
+        print("conftest")
+        def pytest_configure():
+            import django
+            print("pytest_configure: conftest")
+            django.setup = lambda: SHOULD_NOT_GET_CALLED
+    ''')
+
+    django_testdir.project_root.join('tpkg', 'plugin.py').write(dedent('''
+        import pytest
+        import django.apps
+        assert not django.apps.apps.ready
+
+        print("plugin")
+        def pytest_configure():
+            assert django.apps.apps.ready
+            from tpkg.app.models import Item
+            print("pytest_configure: plugin")
+
+        @pytest.hookimpl(tryfirst=True)
+        def pytest_load_initial_conftests(early_config, parser, args):
+            print("pytest_load_initial_conftests")
+            assert not django.apps.apps.ready
+    '''))
+    django_testdir.makepyfile("""
+        def test_ds():
+            pass
+    """)
+    result = django_testdir.runpytest_subprocess('-s', '-p', 'tpkg.plugin')
+    result.stdout.fnmatch_lines([
+        'plugin',
+        'pytest_load_initial_conftests',
+        'conftest',
+        'pytest_configure: conftest',
+        'pytest_configure: plugin',
+        '*1 passed*',
+    ])
+    assert result.ret == 0