timeout: Add test coverage.

tools/test-backend

@@ -101,7 +101,6 @@ not_yet_fully_covered = [
     "zerver/lib/queue.py",
     "zerver/lib/sqlalchemy_utils.py",
     "zerver/lib/storage.py",
-    "zerver/lib/timeout.py",
     "zerver/lib/unminify.py",
     "zerver/lib/utils.py",
     "zerver/lib/zephyr.py",

zerver/tests/test_timeout.py

@@ -0,0 +1,53 @@
+import time
+import traceback
+
+from zerver.lib.test_classes import ZulipTestCase
+from zerver.lib.timeout import TimeoutExpired, timeout
+
+
+class TimeoutTestCase(ZulipTestCase):
+    # We can't use assertRaises because that doesn't store the
+    # traceback, which we want to verify
+
+    def something_exceptional(self) -> int:
+        raise ValueError("Something went wrong")
+
+    def sleep_x_seconds_y_times(self, x: float, y: int) -> int:
+        for i in range(y):
+            time.sleep(x)
+        return 42  # nocoverage
+
+    def test_timeout_returns(self) -> None:
+        ret = timeout(1, lambda: 42)
+        self.assertEqual(ret, 42)
+
+    def test_timeout_exceeded(self) -> None:
+        try:
+            timeout(1, lambda: self.sleep_x_seconds_y_times(0.1, 50))
+            raise AssertionError("Failed to raise a timeout")
+        except TimeoutExpired as exc:
+            tb = traceback.format_tb(exc.__traceback__)
+            self.assertIn("in sleep_x_seconds_y_times", tb[-1])
+            self.assertIn("time.sleep(x)", tb[-1])
+
+    def test_timeout_raises(self) -> None:
+        try:
+            timeout(1, lambda: self.something_exceptional())
+            raise AssertionError("Failed to raise an exception")
+        except ValueError as exc:
+            tb = traceback.format_tb(exc.__traceback__)
+            self.assertIn("in something_exceptional", tb[-1])
+            self.assertIn("raise ValueError", tb[-1])
+
+    def test_timeout_warn(self) -> None:
+        # If the sleep is long enough, it will outlast the attempts to
+        # kill it
+        with self.assertLogs(level="WARNING") as m:
+            try:
+                timeout(1, lambda: self.sleep_x_seconds_y_times(5, 1))
+                raise AssertionError("Failed to raise a timeout")
+            except TimeoutExpired as exc:
+                tb = traceback.format_tb(exc.__traceback__)
+                self.assertNotIn("in sleep_x_seconds_y_times", tb[-1])
+                self.assertIn("raise TimeoutExpired", tb[-1])
+        self.assertEqual(m.output, ["WARNING:root:Failed to time out backend thread"])