also warn on awaitable or async iterable test results

src/_pytest/python.py

@@ -151,10 +151,7 @@ def pytest_configure(config):
 
 @hookimpl(trylast=True)
 def pytest_pyfunc_call(pyfuncitem):
-    testfunction = pyfuncitem.obj
-    if iscoroutinefunction(testfunction) or (
-        sys.version_info >= (3, 6) and inspect.isasyncgenfunction(testfunction)
-    ):
+    def async_warn():
         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"
@@ -162,9 +159,17 @@ def pytest_pyfunc_call(pyfuncitem):
         msg += "  - pytest-tornasync"
         warnings.warn(PytestUnhandledCoroutineWarning(msg.format(pyfuncitem.nodeid)))
         skip(msg="async def function and no async plugin installed (see warnings)")
+
+    testfunction = pyfuncitem.obj
+    if iscoroutinefunction(testfunction) or (
+        sys.version_info >= (3, 6) and inspect.isasyncgenfunction(testfunction)
+    ):
+        async_warn()
     funcargs = pyfuncitem.funcargs
     testargs = {arg: funcargs[arg] for arg in pyfuncitem._fixtureinfo.argnames}
-    testfunction(**testargs)
+    result = testfunction(**testargs)
+    if hasattr(result, "__await__") or hasattr(result, "__aiter__"):
+        async_warn()
     return True
 
 

testing/acceptance_test.py

@@ -1192,6 +1192,8 @@ def test_warn_on_async_function(testdir):
             pass
         async def test_2():
             pass
+        def test_3():
+            return test_2()
     """
     )
     result = testdir.runpytest()
@@ -1199,8 +1201,9 @@ def test_warn_on_async_function(testdir):
         [
             "test_async.py::test_1",
             "test_async.py::test_2",
+            "test_async.py::test_3",
             "*async def functions are not natively supported*",
-            "*2 skipped, 2 warnings in*",
+            "*3 skipped, 3 warnings in*",
         ]
     )
     # ensure our warning message appears only once
@@ -1220,6 +1223,8 @@ def test_warn_on_async_gen_function(testdir):
             yield
         async def test_2():
             yield
+        def test_3():
+            return test_2()
     """
     )
     result = testdir.runpytest()
@@ -1227,8 +1232,9 @@ def test_warn_on_async_gen_function(testdir):
         [
             "test_async.py::test_1",
             "test_async.py::test_2",
+            "test_async.py::test_3",
             "*async def functions are not natively supported*",
-            "*2 skipped, 2 warnings in*",
+            "*3 skipped, 3 warnings in*",
         ]
     )
     # ensure our warning message appears only once