kvserver: remove TestProcessSplitAfterRightHandSideHasBeenRemoved

The test had a race condition between lease transfer verification and
partition activation. After transferring the lease from n1 to n3, there
was a window where n1 could re-acquire the lease before the partition
was activated, causing the subsequent increment to hang waiting for a
slow proposal on the now-partitioned n1.

I spent a couple of hours trying to deflake this, but whenever you fix
one thing, another springs up. This test is not maintainable, and is
highly complex.

The [split_pre_apply] tests cover this functionality. Testing it from "far
away" does give some extra coverage, but at a steep price for maintainability,
which we are not ready to pay, so the test is removed in this commit.

[split_pre_apply]: https://github.com/tbg/cockroach/blob/7270a51a0430999661ed15320527ccc04d796a14/pkg/kv/kvserver/testdata/replica_lifecycle/split_pre_apply.txt

Fixes (on 26.1) #159676
Fixes #158295.

Author: tbg

pkg/kv/kvserver/client_raft_helpers_test.go

@@ -292,44 +292,19 @@ func setupPartitionedRangeWithHandlers(
 	return pr, nil
 }
 
-func (pr *testClusterPartitionedRange) deactivate() { pr.set(false) }
-func (pr *testClusterPartitionedRange) activate()   { pr.set(true) }
+func (pr *testClusterPartitionedRange) activate() { pr.set(true) }
 func (pr *testClusterPartitionedRange) set(active bool) {
 	pr.mu.Lock()
 	defer pr.mu.Unlock()
 	pr.mu.partitioned = active
 }
 
-func (pr *testClusterPartitionedRange) addReplica(replicaID roachpb.ReplicaID) {
-	pr.mu.Lock()
-	defer pr.mu.Unlock()
-	pr.mu.partitionedReplicas[replicaID] = true
-}
-
 func (pr *testClusterPartitionedRange) addStore(storeID roachpb.StoreID) {
 	pr.mu.Lock()
 	defer pr.mu.Unlock()
 	pr.mu.partitionedStores[storeID] = true
 }
 
-func (pr *testClusterPartitionedRange) removeStore(storeID roachpb.StoreID) {
-	pr.mu.Lock()
-	defer pr.mu.Unlock()
-
-	pr.mu.partitionedStores[storeID] = false
-}
-
-func (pr *testClusterPartitionedRange) extend(
-	tc *testcluster.TestCluster,
-	rangeID roachpb.RangeID,
-	replicaID roachpb.ReplicaID,
-	partitionedNode int,
-	activated bool,
-	funcs kvtestutils.UnreliableRaftHandlerFuncs,
-) (*testClusterPartitionedRange, error) {
-	return setupPartitionedRangeWithHandlers(tc, rangeID, replicaID, partitionedNode, activated, pr.handlers, funcs)
-}
-
 // dropRaftMessagesFrom sets up a Raft message handler on the given server that
 // drops inbound Raft messages from the given range and replica IDs. In addition
 // to raft messages, StoreLiveness messages from the replica IDs' store are also