test-network: add test case for issue #37629

(cherry picked from commit b1bed07d84d76f3ab2f11a42fefce2685dbbe685)
(cherry picked from commit a11a8221019a3c364e783052e18dcf438fa3dace)
(cherry picked from commit 8c2213cf1e2f552ccecf396531e861de4ce77d69)
(cherry picked from commit 5f7efc2)

Author: yuwata

test/test-network/systemd-networkd-tests.py

@@ -4113,6 +4113,21 @@ def test_bond_keep_master(self):
         print(output)
         self.assertRegex(output, 'master bond199')
 
+        # Test case for #37629
+        for _ in range(3):
+            # When a slave leaved from its master bonding interface, the kernel brings down the slave.
+            check_output('ip link set dummy98 nomaster')
+            self.wait_online('dummy98:off')
+
+            # Bring up the interface to check if networkd recognizes the interface has no master now.
+            check_output('ip link set dummy98 up')
+            self.wait_online('dummy98:carrier')
+
+            # We need to first bring down the interface to make it join a bonding interface.
+            check_output('ip link set dummy98 down')
+            check_output('ip link set dummy98 master bond199')
+            self.wait_online('dummy98:enslaved')
+
     def test_bond_active_slave(self):
         copy_network_unit('23-active-slave.network', '23-bond199.network', '25-bond-active-backup-slave.netdev', '12-dummy.netdev')
         start_networkd()