Test: Exception handling in PingDataSubProcess.async_ping

Tests that expected exceptions are handled, but unexpected exceptions
are still raised.

Patches out asyncio.create_subprocess_exec to generate exceptions, which
also means that the external ping command is not called during these
tests.

tests/components/ping/test_helpers.py

@@ -0,0 +1,55 @@
+"""Test the exception handling in subprocess version of async_ping."""
+
+from unittest.mock import patch
+
+import pytest
+
+from homeassistant.components.ping.helpers import PingDataSubProcess
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers import entity_registry as er
+
+from tests.common import MockConfigEntry
+
+
+class MockAsyncSubprocess:
+    """Minimal mock implementation of asyncio.subprocess.Process for exception testing."""
+
+    def __init__(self, killsig=ProcessLookupError, **kwargs) -> None:
+        """Store provided exception type for later."""
+        self.killsig = killsig
+
+    async def communicate(self) -> None:
+        """Fails immediately with a timeout."""
+        raise TimeoutError
+
+    async def kill(self) -> None:
+        """Raise preset exception when called."""
+        raise self.killsig
+
+
+async def test_async_ping_expected_exceptions(
+    hass: HomeAssistant,
+    config_entry: MockConfigEntry,
+    entity_registry: er.EntityRegistry,
+) -> None:
+    """Test PingDataSubProcess.async_ping handles expected exceptions."""
+    with patch("asyncio.create_subprocess_exec", return_value=MockAsyncSubprocess()):
+        # Actual parameters irrelevant, as subprocess will not be created
+        ping = PingDataSubProcess(hass, host="10.10.10.10", count=3, privileged=False)
+        assert await ping.async_ping() is None
+
+
+async def test_async_ping_unexpected_exceptions(
+    hass: HomeAssistant,
+    config_entry: MockConfigEntry,
+    entity_registry: er.EntityRegistry,
+) -> None:
+    """Test PingDataSubProcess.async_ping does not suppress unexpected exceptions."""
+    with patch(
+        "asyncio.create_subprocess_exec",
+        return_value=MockAsyncSubprocess(killsig=KeyboardInterrupt),
+    ):
+        # Actual parameters irrelevant, as subprocess will not be created
+        ping = PingDataSubProcess(hass, host="10.10.10.10", count=3, privileged=False)
+        with pytest.raises(KeyboardInterrupt):
+            assert await ping.async_ping() is None