First pass at unhandled errback reporting

pytest_twisted.py

@@ -1,4 +1,5 @@
 import functools
+import gc
 import inspect
 import sys
 import warnings
@@ -9,6 +10,7 @@
 
 from twisted.internet import error, defer
 from twisted.internet.threads import blockingCallFromThread
+from twisted.logger import globalLogPublisher
 from twisted.python import failure
 
 
@@ -102,6 +104,60 @@ def block_from_thread(d):
     return blockingCallFromThread(_instances.reactor, lambda x: x, d)
 
 
+class _Observer:
+    def __init__(self):
+        self.failures = []
+        self.asserted = False
+
+    def register(self):
+        globalLogPublisher.addObserver(self)
+
+    def __call__(self, event_dict):
+        is_error = event_dict.get('isError')
+        s = 'Unhandled error in Deferred'.lower()
+        log_format = event_dict.get('log_format')
+        if log_format is None:
+            log_format = ''
+        is_unhandled = s in log_format.lower()
+
+        if is_error and is_unhandled:
+            self.failures.append(event_dict)
+
+    def assert_empty(self):
+        self.asserted = True
+
+        gc.collect()
+        globalLogPublisher.removeObserver(self)
+
+        assert self.failures == []
+
+
+@pytest.fixture(scope='function')
+def unhandled_errback_observer():
+    observer = _Observer()
+    observer.register()
+
+    yield observer
+
+    if not observer.asserted:
+        observer.assert_empty()
+
+
+def assert_on_unhandled_errbacks(f):
+    @functools.wraps(f)
+    def wrapped(*args, **kwargs):
+        observer = _Observer()
+        observer.register()
+
+        result = f(*args, **kwargs)
+
+        observer.assert_empty()
+
+        return result
+
+    return wrapped
+
+
 @decorator.decorator
 def inlineCallbacks(fun, *args, **kw):
     return defer.inlineCallbacks(fun)(*args, **kw)

testing/test_basic.py

@@ -696,3 +696,71 @@ def test_succeed():
     testdir.makepyfile(test_file)
     rr = testdir.run(sys.executable, "-m", "pytest", "-v", *cmd_opts)
     assert "WrongReactorAlreadyInstalledError" in rr.stderr.str()
+
+
+def test_no_unhandled_errbacks_to_assert(testdir, cmd_opts):
+    test_file = """
+    def test_fail(unhandled_errback_observer):
+        unhandled_errback_observer.assert_empty()
+    """
+    testdir.makepyfile(test_file)
+    rr = testdir.run(sys.executable, "-m", "pytest", *cmd_opts)
+    assert_outcomes(rr, {"passed": 1, "error": None})
+
+
+def test_an_unhandled_errback_to_auto_assert(testdir, cmd_opts):
+    test_file = """
+    from twisted.internet.defer import Deferred
+
+    def test_fail(unhandled_errback_observer):
+        d = Deferred()
+        d.errback(42)
+    """
+    testdir.makepyfile(test_file)
+    rr = testdir.run(sys.executable, "-m", "pytest", *cmd_opts)
+    assert_outcomes(rr, {"passed": 1, "error": 1})
+
+
+def test_an_unhandled_errback_to_manually_assert(testdir, cmd_opts):
+    test_file = """
+    from twisted.internet.defer import Deferred
+
+    def test_fail(unhandled_errback_observer):
+        d = Deferred()
+        d.errback(42)
+
+        del d
+        unhandled_errback_observer.assert_empty()
+    """
+    testdir.makepyfile(test_file)
+    rr = testdir.run(sys.executable, "-m", "pytest", *cmd_opts)
+    assert_outcomes(rr, {"failed": 1})
+
+
+def test_no_unhandled_errbacks_to_assert_decorator(testdir, cmd_opts):
+    test_file = """
+    import pytest_twisted
+
+    @pytest_twisted.assert_on_unhandled_errbacks
+    def test_fail():
+        pass
+    """
+    testdir.makepyfile(test_file)
+    rr = testdir.run(sys.executable, "-m", "pytest", *cmd_opts)
+    assert_outcomes(rr, {"passed": 1})
+
+
+def test_an_unhandled_errback_to_assert_decorator(testdir, cmd_opts):
+    test_file = """
+    from twisted.internet.defer import Deferred
+
+    import pytest_twisted
+
+    @pytest_twisted.assert_on_unhandled_errbacks
+    def test_fail():
+        d = Deferred()
+        d.errback(42)
+    """
+    testdir.makepyfile(test_file)
+    rr = testdir.run(sys.executable, "-m", "pytest", *cmd_opts)
+    assert_outcomes(rr, {"failed": 1})