Issue a warning for async gen functions

Co-Authored-By: Bruno Oliveira <nicoddemus@gmail.com>

changelog/5734.bugfix.rst

@@ -0,0 +1 @@
+Skip async generator test functions, and update the warning message to refer to ``async def`` functions.

src/_pytest/compat.py

@@ -40,14 +40,16 @@ def is_generator(func):
 
 
 def iscoroutinefunction(func):
-    """Return True if func is a decorated coroutine function.
-
-    Note: copied and modified from Python 3.5's builtin couroutines.py to avoid import asyncio directly,
-    which in turns also initializes the "logging" module as side-effect (see issue #8).
     """
-    return getattr(func, "_is_coroutine", False) or (
-        hasattr(inspect, "iscoroutinefunction") and inspect.iscoroutinefunction(func)
-    )
+    Return True if func is a coroutine function (a function defined with async
+    def syntax, and doesn't contain yield), or a function decorated with
+    @asyncio.coroutine.
+
+    Note: copied and modified from Python 3.5's builtin couroutines.py to avoid
+    importing asyncio directly, which in turns also initializes the "logging"
+    module as a side-effect (see issue #8).
+    """
+    return inspect.iscoroutinefunction(func) or getattr(func, "_is_coroutine", False)
 
 
 def getlocation(function, curdir):

src/_pytest/python.py

@@ -23,6 +23,7 @@ from _pytest.compat import getfslineno
 from _pytest.compat import getimfunc
 from _pytest.compat import getlocation
 from _pytest.compat import is_generator
+from _pytest.compat import iscoroutinefunction
 from _pytest.compat import NOTSET
 from _pytest.compat import REGEX_TYPE
 from _pytest.compat import safe_getattr
@@ -151,15 +152,16 @@ def pytest_configure(config):
 @hookimpl(trylast=True)
 def pytest_pyfunc_call(pyfuncitem):
     testfunction = pyfuncitem.obj
-    iscoroutinefunction = getattr(inspect, "iscoroutinefunction", None)
-    if iscoroutinefunction is not None and iscoroutinefunction(testfunction):
-        msg = "Coroutine functions are not natively supported and have been skipped.\n"
+    if iscoroutinefunction(testfunction) or (
+        sys.version_info >= (3, 6) and inspect.isasyncgenfunction(testfunction)
+    ):
+        msg = "async def functions are not natively supported and have been skipped.\n"
         msg += "You need to install a suitable plugin for your async framework, for example:\n"
         msg += "  - pytest-asyncio\n"
         msg += "  - pytest-trio\n"
         msg += "  - pytest-tornasync"
         warnings.warn(PytestUnhandledCoroutineWarning(msg.format(pyfuncitem.nodeid)))
-        skip(msg="coroutine function and no async plugin installed (see warnings)")
+        skip(msg="async def function and no async plugin installed (see warnings)")
     funcargs = pyfuncitem.funcargs
     testargs = {arg: funcargs[arg] for arg in pyfuncitem._fixtureinfo.argnames}
     testfunction(**testargs)

testing/acceptance_test.py

@@ -1199,11 +1199,39 @@ def test_warn_on_async_function(testdir):
         [
             "test_async.py::test_1",
             "test_async.py::test_2",
-            "*Coroutine functions are not natively supported*",
+            "*async def functions are not natively supported*",
             "*2 skipped, 2 warnings in*",
         ]
     )
     # ensure our warning message appears only once
     assert (
-        result.stdout.str().count("Coroutine functions are not natively supported") == 1
+        result.stdout.str().count("async def functions are not natively supported") == 1
+    )
+
+
+@pytest.mark.filterwarnings("default")
+@pytest.mark.skipif(
+    sys.version_info < (3, 6), reason="async gen syntax available in Python 3.6+"
+)
+def test_warn_on_async_gen_function(testdir):
+    testdir.makepyfile(
+        test_async="""
+        async def test_1():
+            yield
+        async def test_2():
+            yield
+    """
+    )
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(
+        [
+            "test_async.py::test_1",
+            "test_async.py::test_2",
+            "*async def functions are not natively supported*",
+            "*2 skipped, 2 warnings in*",
+        ]
+    )
+    # ensure our warning message appears only once
+    assert (
+        result.stdout.str().count("async def functions are not natively supported") == 1
     )

testing/test_compat.py

@@ -91,9 +91,6 @@ def test_is_generator_asyncio(testdir):
     result.stdout.fnmatch_lines(["*1 passed*"])
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 5), reason="async syntax available in Python 3.5+"
-)
 def test_is_generator_async_syntax(testdir):
     testdir.makepyfile(
         """
@@ -113,6 +110,29 @@ def test_is_generator_async_syntax(testdir):
     result.stdout.fnmatch_lines(["*1 passed*"])
 
 
+@pytest.mark.skipif(
+    sys.version_info < (3, 6), reason="async gen syntax available in Python 3.6+"
+)
+def test_is_generator_async_gen_syntax(testdir):
+    testdir.makepyfile(
+        """
+        from _pytest.compat import is_generator
+        def test_is_generator_py36():
+            async def foo():
+                yield
+                await foo()
+
+            async def bar():
+                yield
+
+            assert not is_generator(foo)
+            assert not is_generator(bar)
+    """
+    )
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(["*1 passed*"])
+
+
 class ErrorsHelper:
     @property
     def raise_exception(self):