test-network: add a test case for [IPv6Prefix] Assign=yes

test/test-network/conf/ipv6ra-prefix.network

@@ -4,10 +4,13 @@ Name=veth99
 [Network]
 DHCP=no
 IPv6PrefixDelegation=yes
-Address=2001:db8:0:1::1/64
 
 [IPv6Prefix]
-Prefix=2001:db8:0:1::4/64
+Prefix=2001:db8:0:1::/64
+
+[IPv6Prefix]
+Prefix=2001:db8:0:2::/64
+Assign=yes
 
 [IPv6RoutePrefix]
 Route=2001:db0:fff::/64

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

@@ -3575,10 +3575,15 @@ class NetworkdIPv6PrefixTests(unittest.TestCase, Utilities):
         start_networkd()
         self.wait_online(['veth99:routable', 'veth-peer:routable'])
 
-        output = check_output('ip', '-6', 'route', 'show', 'dev', 'veth-peer')
+        output = check_output('ip -6 route show dev veth-peer')
         print(output)
         self.assertRegex(output, '2001:db8:0:1::/64 proto ra')
 
+        output = check_output('ip addr show dev veth99')
+        print(output)
+        self.assertNotRegex(output, '2001:db8:0:1')
+        self.assertRegex(output, '2001:db8:0:2')
+
 class NetworkdMTUTests(unittest.TestCase, Utilities):
     links = ['dummy98']