selftests/tc-testing: add show class case for red qdisc

Test 290a: Show RED class
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/tc-testing/tc-tests/qdiscs/red.json

@@ -181,5 +181,28 @@
             "$TC qdisc del dev $DUMMY handle 1: root",
             "$IP link del dev $DUMMY type dummy"
         ]
+    },
+    {
+        "id": "290a",
+        "name": "Show RED class",
+        "category": [
+            "qdisc",
+            "red"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link add dev $DUMMY type dummy || /bin/true"
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root red limit 1M avpkt 1500 min 100K max 300K",
+        "expExitCode": "0",
+        "verifyCmd": "$TC class show dev $DUMMY",
+        "matchPattern": "class red 1:[0-9]+ parent 1:",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root",
+            "$IP link del dev $DUMMY type dummy"
+        ]
     }
 ]