Test the exception-handling case of ReactorBuilder.buildReactor

src/twisted/internet/test/test_reactormixins.py

@@ -0,0 +1,61 @@
+"""
+Tests L{twisted.internet.test.reactormixins}, the reactor-testing support
+module.
+"""
+
+from hamcrest import assert_that, equal_to, has_length
+from typing_extensions import NoReturn
+
+# Trial should expose matches_result publically.
+# https://github.com/twisted/twisted/issues/11709
+from twisted.trial._dist.test.matchers import matches_result
+from twisted.trial.reporter import TestResult
+from twisted.trial.runner import TestLoader
+from twisted.trial.unittest import SynchronousTestCase, TestSuite
+from .reactormixins import ReactorBuilder
+
+UNSUPPORTED = "This reactor is unsupported."
+
+
+def unsupportedReactor(self: ReactorBuilder) -> NoReturn:
+    """
+    A function that can be used as a factory for L{ReactorBuilder} tests but
+    which always raises an exception.
+
+    This gives the appearance of a reactor type which is unsupported in the
+    current runtime configuration for some reason.
+    """
+    raise Exception(UNSUPPORTED)
+
+
+class ReactorBuilderTests(SynchronousTestCase):
+    """
+    Tests for L{ReactorBuilder}.
+    """
+
+    def test_buildReactorFails(self) -> None:
+        """
+        If the reactor factory raises any exception then
+        L{ReactorBuilder.buildReactor} raises L{SkipTest}.
+        """
+
+        class BrokenReactorFactory(ReactorBuilder, SynchronousTestCase):
+            _reactors = [
+                "twisted.internet.test.test_reactormixins.unsupportedReactor",
+            ]
+
+            def test_brokenFactory(self) -> None:
+                """
+                Try, and fail, to build an unsupported reactor.
+                """
+                self.buildReactor()
+
+        cases = BrokenReactorFactory.makeTestCaseClasses().values()
+        loader = TestLoader()
+        suite = TestSuite(loader.loadClass(cls) for cls in cases)
+        result = TestResult()
+        suite.run(result)
+
+        assert_that(result, matches_result(skips=has_length(1)))
+        [(_, skip)] = result.skips
+        assert_that(skip, equal_to(UNSUPPORTED))