测试：覆盖USB设备挂载与失败回滚

tools/tests/test_usb_device_qmp.py

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+import importlib.util
+from pathlib import Path
+import unittest
+
+spec = importlib.util.spec_from_file_location("usb_qmp", Path(__file__).parents[1] / "usb-device-qmp.py")
+usb = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(usb)
+
+
+class FakeQmp:
+    def __init__(self, occupied=False, fail_add=False):
+        self.calls = []
+        self.occupied = occupied
+        self.fail_add = fail_add
+
+    def call(self, name, args=None):
+        self.calls.append((name, args))
+        if name == "query-chardev":
+            return [{"label": "vdi_usb_box_100"}] if self.occupied else []
+        if name == "qom-list":
+            return [{"name": "tablet"}, {"name": "hostpci0"}]
+        if name == "device_add" and self.fail_add:
+            raise RuntimeError("bad USB bus")
+        return {}
+
+
+class UsbQmpTests(unittest.TestCase):
+    def test_only_loopback_tunnel_and_approved_storage_are_attached(self):
+        q = FakeQmp()
+        usb.attach(q, 100, 40001, "ehci-2.0", "0951", "1666")
+        channel = next(a for n, a in q.calls if n == "chardev-add")
+        self.assertEqual(channel["backend"]["data"]["addr"]["data"]["host"], "127.0.0.1")
+        device = next(a for n, a in q.calls if n == "device_add")
+        self.assertEqual(device["filter"], "0x08:0x0951:0x1666:-1:1|-1:-1:-1:-1:0")
+
+    def test_busy_endpoint_is_never_replaced(self):
+        q = FakeQmp(occupied=True)
+        with self.assertRaisesRegex(RuntimeError, "already exists"):
+            usb.attach(q, 100, 40001, "ehci-2.0", "0951", "1666")
+        self.assertFalse(any(n in ("chardev-add", "chardev-remove", "device_del") for n, _ in q.calls))
+
+    def test_failed_device_add_rolls_back_only_its_new_channel(self):
+        q = FakeQmp(fail_add=True)
+        with self.assertRaisesRegex(RuntimeError, "bad USB bus"):
+            usb.attach(q, 100, 40001, "ehci-2.0", "0951", "1666")
+        self.assertEqual(q.calls[-1], ("chardev-remove", {"id": "vdi_usb_box_100"}))
+
+
+if __name__ == "__main__":
+    unittest.main()