Add mechanism for explicit marking of fixtures which should be run with asyncio

README.rst

@@ -39,6 +39,9 @@ Features
 - pytest markers for treating tests as asyncio coroutines
 - easy testing with non-default event loops
 - support for `async def` fixtures and async generator fixtures
+- support *auto* mode to handle all async fixtures and tests automatically by asyncio;
+  provide *strict* mode if a test suite should work with different async frameworks
+  simultaneously, e.g. ``asyncio`` and ``trio``.
 
 Installation
 ------------
@@ -51,6 +54,70 @@ To install pytest-asyncio, simply:
 
 This is enough for pytest to pick up pytest-asyncio.
 
+Modes
+-----
+
+Starting from ``pytest-asyncio>=0.17``, three modes are provided: *auto*, *strict* and
+*legacy* (default).
+
+The mode can be set by ``asyncio_mode`` configuration option in `configuration file
+<https://docs.pytest.org/en/latest/reference/customize.html>`_:
+
+.. code-block:: ini
+
+   # pytest.ini
+   [pytest]
+   asyncio_mode = auto
+
+The value can be overriden by command-line option for ``pytest`` invocation:
+
+.. code-block:: bash
+
+   $ pytest tests --asyncio-mode=strict
+
+Auto mode
+~~~~~~~~~
+
+When the mode is auto, all discovered *async* tests are considered *asyncio-driven* even
+if they have no ``@pytest.mark.asyncio`` marker.
+
+All async fixtures are considered *asyncio-driven* as well, even if they are decorated
+with a regular ``@pytest.fixture`` decorator instead of dedicated
+``@pytest_asyncio.fixture`` counterpart.
+
+*asyncio-driven* means that tests and fixtures are executed by ``pytest-asyncio``
+plugin.
+
+This mode requires the simplest tests and fixtures configuration and is
+recommended for default usage *unless* the same project and its test suite should
+execute tests from different async frameworks, e.g. ``asyncio`` and ``trio``.  In this
+case, auto-handling can break tests designed for other framework; plase use *strict*
+mode instead.
+
+Strict mode
+~~~~~~~~~~~
+
+Strict mode enforces ``@pytest.mark.asyncio`` and ``@pytest_asyncio.fixture`` usage.
+Without these markers, tests and fixtures are not considered as *asyncio-driven*, other
+pytest plugin can handle them.
+
+Please use this mode if multiple async frameworks should be combined in the same test
+suite.
+
+
+Legacy mode
+~~~~~~~~~~~
+
+This mode follows rules used by ``pytest-asyncio<0.17``: tests are not auto-marked but
+fixtures are.
+
+This mode is used by default for the sake of backward compatibility, deprecation
+warnings are emitted with suggestion to either switching to ``auto`` mode or using
+``strict`` mode with ``@pytest_asyncio.fixture`` decorators.
+
+In future, the default will be changed.
+
+
 Fixtures
 --------
 
@@ -116,16 +183,18 @@ Work just like their TCP counterparts but return unused UDP ports.
 
 Async fixtures
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Asynchronous fixtures are defined just like ordinary pytest fixtures, except they should be coroutines or asynchronous generators.
+Asynchronous fixtures are defined just like ordinary pytest fixtures, except they should be decorated with ``@pytest_asyncio.fixture``.
 
 .. code-block:: python3
 
-    @pytest.fixture
+    import pytest_asyncio
+
+    @pytest_asyncio.fixture
     async def async_gen_fixture():
         await asyncio.sleep(0.1)
         yield 'a value'
 
-    @pytest.fixture(scope='module')
+    @pytest_asyncio.fixture(scope='module')
     async def async_fixture():
         return await asyncio.sleep(0.1)
 
@@ -134,6 +203,9 @@ to redefine the ``event_loop`` fixture to have the same or broader scope.
 Async fixtures need the event loop, and so must have the same or narrower scope
 than the ``event_loop`` fixture.
 
+*auto* and *legacy* mode automatically converts async fixtures declared with the
+standard ``@pytest.fixture`` decorator to *asyncio-driven* versions.
+
 
 Markers
 -------
@@ -164,6 +236,10 @@ Only test coroutines will be affected (by default, coroutines prefixed by
         """No marker!"""
         await asyncio.sleep(0, loop=event_loop)
 
+In *auto* mode, the ``pytest.mark.asyncio`` marker can be omitted, the marker is added
+automatically to *async* test functions.
+
+
 .. |pytestmark| replace:: ``pytestmark``
 .. _pytestmark: http://doc.pytest.org/en/latest/example/markers.html#marking-whole-classes-or-modules
 

pytest_asyncio/__init__.py

@@ -1,2 +1,7 @@
 """The main point for importing pytest-asyncio items."""
 __version__ = "0.16.0"
+
+from .plugin import fixture
+
+
+__all__ = ("fixture",)

pytest_asyncio/plugin.py

@@ -1,20 +1,106 @@
 """pytest-asyncio implementation."""
 import asyncio
 import contextlib
+import enum
 import functools
 import inspect
 import socket
+import sys
+import warnings
 
 import pytest
 
-from inspect import isasyncgenfunction
+
+class Mode(str, enum.Enum):
+    AUTO = "auto"
+    STRICT = "strict"
+    LEGACY = "legacy"
+
+
+LEGACY_MODE = pytest.PytestDeprecationWarning(
+    "The 'asyncio_mode' default value will change to 'strict' in future, "
+    "please explicitly use 'asyncio_mode=strict' or 'asyncio_mode=auto' "
+    "in pytest configuration file."
+)
+
+LEGACY_ASYNCIO_FIXTURE = (
+    "'@pytest.fixture' is applied to {name} "
+    "in 'legacy' mode, "
+    "please replace it with '@pytest_asyncio.fixture' as a preparation "
+    "for switching to 'strict' mode (or use 'auto' mode to seamlessly handle "
+    "all these fixtures as asyncio-driven)."
+)
+
+
+ASYNCIO_MODE_HELP = """\
+'auto' - for automatically handling all async functions by the plugin
+'strict' - for autoprocessing disabling (useful if different async frameworks \
+should be tested together, e.g. \
+both pytest-asyncio and pytest-trio are used in the same project)
+'legacy' - for keeping compatibility with pytest-asyncio<0.17: \
+auto-handling is disabled but pytest_asyncio.fixture usage is not enforced
+"""
+
+
+def pytest_addoption(parser, pluginmanager):
+    group = parser.getgroup("asyncio")
+    group.addoption(
+        "--asyncio-mode",
+        dest="asyncio_mode",
+        default=None,
+        metavar="MODE",
+        help=ASYNCIO_MODE_HELP,
+    )
+    parser.addini(
+        "asyncio_mode",
+        help="default value for --asyncio-mode",
+        type="string",
+        default="legacy",
+    )
+
+
+def fixture(fixture_function=None, **kwargs):
+    if fixture_function is not None:
+        _set_explicit_asyncio_mark(fixture_function)
+        return pytest.fixture(fixture_function, **kwargs)
+
+    else:
+
+        @functools.wraps(fixture)
+        def inner(fixture_function):
+            return fixture(fixture_function, **kwargs)
+
+        return inner
+
+
+def _has_explicit_asyncio_mark(obj):
+    obj = getattr(obj, "__func__", obj)  # instance method maybe?
+    return getattr(obj, "_force_asyncio_fixture", False)
+
+
+def _set_explicit_asyncio_mark(obj):
+    if hasattr(obj, "__func__"):
+        # instance method, check the function object
+        obj = obj.__func__
+    obj._force_asyncio_fixture = True
 
 
 def _is_coroutine(obj):
     """Check to see if an object is really an asyncio coroutine."""
     return asyncio.iscoroutinefunction(obj) or inspect.isgeneratorfunction(obj)
 
 
+def _is_coroutine_or_asyncgen(obj):
+    return _is_coroutine(obj) or inspect.isasyncgenfunction(obj)
+
+
+def _get_asyncio_mode(config):
+    val = config.getoption("asyncio_mode")
+    if val is None:
+        val = config.getini("asyncio_mode")
+    return Mode(val)
+
+
 def pytest_configure(config):
     """Inject documentation."""
     config.addinivalue_line(
@@ -23,6 +109,22 @@ def pytest_configure(config):
         "mark the test as a coroutine, it will be "
         "run using an asyncio event loop",
     )
+    if _get_asyncio_mode(config) == Mode.LEGACY:
+        _issue_warning_captured(LEGACY_MODE, config.hook, stacklevel=1)
+
+
+def _issue_warning_captured(warning, hook, *, stacklevel=1):
+    # copy-paste of pytest internal _pytest.warnings._issue_warning_captured function
+    with warnings.catch_warnings(record=True) as records:
+        warnings.simplefilter("always", type(warning))
+        warnings.warn(LEGACY_MODE, stacklevel=stacklevel)
+    frame = sys._getframe(stacklevel - 1)
+    location = frame.f_code.co_filename, frame.f_lineno, frame.f_code.co_name
+    hook.pytest_warning_recorded.call_historic(
+        kwargs=dict(
+            warning_message=records[0], when="config", nodeid="", location=location
+        )
+    )
 
 
 @pytest.mark.tryfirst
@@ -32,6 +134,13 @@ def pytest_pycollect_makeitem(collector, name, obj):
         item = pytest.Function.from_parent(collector, name=name)
         if "asyncio" in item.keywords:
             return list(collector._genfunctions(name, obj))
+        else:
+            if _get_asyncio_mode(item.config) == Mode.AUTO:
+                # implicitly add asyncio marker if asyncio mode is on
+                ret = list(collector._genfunctions(name, obj))
+                for elem in ret:
+                    elem.add_marker("asyncio")
+                return ret
 
 
 class FixtureStripper:
@@ -88,9 +197,42 @@ def pytest_fixture_setup(fixturedef, request):
         policy.set_event_loop(loop)
         return
 
-    if isasyncgenfunction(fixturedef.func):
+    func = fixturedef.func
+    if not _is_coroutine_or_asyncgen(func):
+        # Nothing to do with a regular fixture function
+        yield
+        return
+
+    config = request.node.config
+    asyncio_mode = _get_asyncio_mode(config)
+
+    if not _has_explicit_asyncio_mark(func):
+        if asyncio_mode == Mode.AUTO:
+            # Enforce asyncio mode if 'auto'
+            _set_explicit_asyncio_mark(func)
+        elif asyncio_mode == Mode.LEGACY:
+            _set_explicit_asyncio_mark(func)
+            try:
+                code = func.__code__
+            except AttributeError:
+                code = func.__func__.__code__
+            name = (
+                f"<fixture {func.__qualname__}, file={code.co_filename}, "
+                f"line={code.co_firstlineno}>"
+            )
+            warnings.warn(
+                LEGACY_ASYNCIO_FIXTURE.format(name=name),
+                pytest.PytestDeprecationWarning,
+            )
+        else:
+            # asyncio_mode is STRICT,
+            # don't handle fixtures that are not explicitly marked
+            yield
+            return
+
+    if inspect.isasyncgenfunction(func):
         # This is an async generator function. Wrap it accordingly.
-        generator = fixturedef.func
+        generator = func
 
         fixture_stripper = FixtureStripper(fixturedef)
         fixture_stripper.add(FixtureStripper.EVENT_LOOP)
@@ -129,8 +271,8 @@ async def async_finalizer():
             return loop.run_until_complete(setup())
 
         fixturedef.func = wrapper
-    elif inspect.iscoroutinefunction(fixturedef.func):
-        coro = fixturedef.func
+    elif inspect.iscoroutinefunction(func):
+        coro = func
 
         fixture_stripper = FixtureStripper(fixturedef)
         fixture_stripper.add(FixtureStripper.EVENT_LOOP)

setup.cfg

@@ -7,6 +7,7 @@ show_missing = true
 [tool:pytest]
 addopts = -rsx --tb=short
 testpaths = tests
+asyncio_mode = auto
 filterwarnings = error
 
 [metadata]