make async tests and tests that return non-None fail instead of warn

src/_pytest/config/exceptions.py

@@ -1,7 +1,3 @@
-from typing import final
-
-
-@final
 class UsageError(Exception):
     """Error in pytest usage or invocation."""
 

src/_pytest/python.py

@@ -54,6 +54,7 @@
 from _pytest.config import Config
 from _pytest.config import hookimpl
 from _pytest.config.argparsing import Parser
+from _pytest.config.exceptions import UsageError
 from _pytest.deprecated import check_ispytest
 from _pytest.fixtures import FixtureDef
 from _pytest.fixtures import FixtureRequest
@@ -77,7 +78,6 @@
 from _pytest.stash import StashKey
 from _pytest.warning_types import PytestCollectionWarning
 from _pytest.warning_types import PytestReturnNotNoneWarning
-from _pytest.warning_types import PytestUnhandledCoroutineWarning
 
 
 if TYPE_CHECKING:
@@ -138,6 +138,16 @@ def pytest_configure(config: Config) -> None:
     )
 
 
+@final
+class PytestUnhandledCoroutineError(UsageError):
+    """An unraisable exception resulted in an error.
+
+    Unraisable exceptions are exceptions raised in :meth:`__del__ <object.__del__>`
+    implementations and similar situations when the exception cannot be raised
+    as normal.
+    """
+
+
 def async_warn_and_skip(nodeid: str) -> None:
     msg = "async def functions are not natively supported and have been skipped.\n"
     msg += (
@@ -148,7 +158,9 @@ def async_warn_and_skip(nodeid: str) -> None:
     msg += "  - pytest-tornasync\n"
     msg += "  - pytest-trio\n"
     msg += "  - pytest-twisted"
-    warnings.warn(PytestUnhandledCoroutineWarning(msg.format(nodeid)))
+    raise PytestUnhandledCoroutineError(
+        msg.format(nodeid)
+    )  # TODO: This is the warning to look at
     skip(reason="async def function and no async plugin installed (see warnings)")
 
 

src/_pytest/warning_types.py

@@ -77,7 +77,7 @@ def simple(cls, apiname: str) -> "PytestExperimentalApiWarning":
 
 
 @final
-class PytestUnhandledCoroutineWarning(PytestReturnNotNoneWarning):
+class PytestUnhandledCoroutineWarning(PytestReturnNotNoneWarning):  # TODO: look at this
     """Warning emitted for an unhandled coroutine.
 
     A coroutine was encountered when collecting test functions, but was not

testing/acceptance_test.py

@@ -1233,7 +1233,7 @@ def test_usage_error_code(pytester: Pytester) -> None:
     assert result.ret == ExitCode.USAGE_ERROR
 
 
-def test_warn_on_async_function(pytester: Pytester) -> None:
+def test_error_on_async_function(pytester: Pytester) -> None:  # TODO: Change this
     # In the below we .close() the coroutine only to avoid
     # "RuntimeWarning: coroutine 'test_2' was never awaited"
     # which messes with other tests.
@@ -1249,23 +1249,19 @@ def test_3():
             return coro
     """
     )
-    result = pytester.runpytest("-Wdefault")
+    result = pytester.runpytest()
     result.stdout.fnmatch_lines(
         [
-            "test_async.py::test_1",
-            "test_async.py::test_2",
-            "test_async.py::test_3",
+            "*test_async.py::test_1*",
+            "*test_async.py::test_2*",
+            "*test_async.py::test_3*",
             "*async def functions are not natively supported*",
-            "*3 skipped, 3 warnings in*",
         ]
     )
-    # ensure our warning message appears only once
-    assert (
-        result.stdout.str().count("async def functions are not natively supported") == 1
-    )
+    result.assert_outcomes(failed=3)
 
 
-def test_warn_on_async_gen_function(pytester: Pytester) -> None:
+def test_error_on_async_gen_function(pytester: Pytester) -> None:  # TODO: Change this
     pytester.makepyfile(
         test_async="""
         async def test_1():
@@ -1276,20 +1272,15 @@ def test_3():
             return test_2()
     """
     )
-    result = pytester.runpytest("-Wdefault")
+    result = pytester.runpytest()
     result.stdout.fnmatch_lines(
         [
-            "test_async.py::test_1",
-            "test_async.py::test_2",
-            "test_async.py::test_3",
+            "*test_async.py::test_1*",
+            "*test_async.py::test_2*",
+            "*test_async.py::test_3*",
             "*async def functions are not natively supported*",
-            "*3 skipped, 3 warnings in*",
         ]
     )
-    # ensure our warning message appears only once
-    assert (
-        result.stdout.str().count("async def functions are not natively supported") == 1
-    )
 
 
 def test_pdb_can_be_rewritten(pytester: Pytester) -> None:

testing/test_unittest.py

@@ -1309,7 +1309,7 @@ def test_1(self):
     assert tracked == []
 
 
-def test_async_support(pytester: Pytester) -> None:
+def test_async_support(pytester: Pytester) -> None:  # TODO: Change this
     pytest.importorskip("unittest.async_case")
 
     pytester.copy_example("unittest/test_unittest_asyncio.py")