review fixes: add test cases to conf_chage

src/governor/cc.rs

@@ -306,7 +306,7 @@ mod tests {
     macro_rules! p_with_tier {
         (
             $raft_id:literal,
-            $tier:literal,
+            $tier:ident,
             $grade:ident
 
         ) => {{
@@ -610,24 +610,26 @@ mod tests {
         );
 
         let mut tiers = HashMap::new();
-        let storage_tier = Tier {
-            name: "storage".into(),
+        const VOTER_TIER_NAME: &str = "voter";
+        const FOLLOWER_TIER_NAME: &str = "follower";
+        let voter_tier = Tier {
+            name: VOTER_TIER_NAME.into(),
             replication_factor: 1,
             can_vote: true,
         };
         let router_tier = Tier {
-            name: "router".into(),
+            name: FOLLOWER_TIER_NAME.into(),
             replication_factor: 1,
             can_vote: false,
         };
-        tiers.insert(storage_tier.name.as_str(), &storage_tier);
+        tiers.insert(voter_tier.name.as_str(), &voter_tier);
         tiers.insert(router_tier.name.as_str(), &router_tier);
 
         assert_eq!(
             cc_with_tiers(
                 &[
-                    p_with_tier!(1, "storage", Online),
-                    p_with_tier!(2, "router", Online),
+                    p_with_tier!(1, VOTER_TIER_NAME, Online),
+                    p_with_tier!(2, FOLLOWER_TIER_NAME, Online),
                 ],
                 &[1],
                 &[2],
@@ -640,8 +642,8 @@ mod tests {
         assert_eq!(
             cc_with_tiers(
                 &[
-                    p_with_tier!(1, "storage", Online),
-                    p_with_tier!(2, "router", Online),
+                    p_with_tier!(1, VOTER_TIER_NAME, Online),
+                    p_with_tier!(2, FOLLOWER_TIER_NAME, Online),
                 ],
                 &[2],
                 &[1],
@@ -650,5 +652,46 @@ mod tests {
             // case when bootstrap leader from tier with falsy `can_vote`
             cc![AddNode(1), RemoveNode(2), AddLearnerNode(2)]
         );
+
+        assert_eq!(
+            cc_with_tiers(
+                &[
+                    p_with_tier!(1, VOTER_TIER_NAME, Expelled),
+                    p_with_tier!(2, FOLLOWER_TIER_NAME, Online),
+                ],
+                &[1],
+                &[2],
+                &tiers
+            ),
+            // remove expelled voter
+            cc![RemoveNode(1)]
+        );
+
+        assert_eq!(
+            cc_with_tiers(
+                &[
+                    p_with_tier!(1, FOLLOWER_TIER_NAME, Expelled),
+                    p_with_tier!(2, FOLLOWER_TIER_NAME, Online),
+                ],
+                &[1],
+                &[2],
+                &tiers
+            ),
+            // remove expelled follower
+            cc![RemoveNode(1)]
+        );
+
+        assert_eq!(
+            cc_with_tiers(
+                &[
+                    p_with_tier!(1, VOTER_TIER_NAME, Online),
+                    p_with_tier!(2, VOTER_TIER_NAME, Online),
+                ],
+                &[],
+                &[1, 2],
+                &tiers
+            ),
+            cc![AddNode(1), AddNode(2)]
+        );
     }
 }