If a fixture cancels the test, that's always a failure

Even if it doesn't raise an exception afterwards.

Author: njsmith

pytest_trio/_tests/test_fixture_mistakes.py

@@ -117,3 +117,32 @@ def test_whatever(async_fixture):
     result.stdout.fnmatch_lines(
         ["*: Trio fixtures can only be used by Trio tests*"]
     )
+
+
+@enable_trio_mode
+def test_fixture_cancels_test_but_doesnt_raise(testdir, enable_trio_mode):
+    enable_trio_mode(testdir)
+
+    testdir.makepyfile(
+        """
+        import pytest
+        import trio
+
+        @pytest.fixture
+        async def async_fixture():
+            with trio.CancelScope() as cscope:
+                cscope.cancel()
+                yield
+
+
+        async def test_whatever(async_fixture):
+            pass
+        """
+    )
+
+    result = testdir.runpytest()
+
+    result.assert_outcomes(failed=1)
+    result.stdout.fnmatch_lines(
+        ["*async_fixture*cancelled the test*"]
+    )

pytest_trio/plugin.py

@@ -133,11 +133,16 @@ class TrioTestContext:
     def __init__(self):
         self.crashed = False
         self.test_cancel_scope = None
+        self.fixtures_with_errors = set()
+        self.fixtures_with_cancel = set()
         self.error_list = []
 
-    def crash(self, exc):
-        if exc is not None:
+    def crash(self, fixture, exc):
+        if exc is None:
+            self.fixtures_with_cancel.add(fixture)
+        else:
             self.error_list.append(exc)
+            self.fixtures_with_errors.add(fixture)
         self.crashed = True
         if self.test_cancel_scope is not None:
             self.test_cancel_scope.cancel()
@@ -193,7 +198,7 @@ async def _fixture_manager(self, test_ctx):
                 finally:
                     nursery_fixture.cancel_scope.cancel()
         except BaseException as exc:
-            test_ctx.crash(exc)
+            test_ctx.crash(self, exc)
         finally:
             self.setup_done.set()
             self._teardown_done.set()
@@ -286,7 +291,7 @@ async def run(self, test_ctx, contextvars_ctx):
             except BaseException as exc:
                 assert isinstance(exc, trio.Cancelled)
                 yield_outcome = outcome.Error(exc)
-                test_ctx.crash(None)
+                test_ctx.crash(self, None)
                 with trio.CancelScope(shield=True):
                     for event in self.user_done_events:
                         await event.wait()
@@ -342,6 +347,19 @@ async def _bootstrap_fixtures_and_run_test(**kwargs):
                     fixture.run, test_ctx, contextvars_ctx, name=fixture.name
                 )
 
+        silent_cancellers = (
+            test_ctx.fixtures_with_cancel - test_ctx.fixtures_with_errors
+        )
+        if silent_cancellers:
+            for fixture in silent_cancellers:
+                test_ctx.error_list.append(
+                    RuntimeError(
+                        "{} cancelled the test but didn't "
+                        "raise an error"
+                        .format(fixture.name)
+                    )
+                )
+
         if test_ctx.error_list:
             raise trio.MultiError(test_ctx.error_list)