tests: Fix cluster version and downgrade request timeout

Returning nil means that raft.Trigger was not called, causing member to
wait infinitly for response for response on raft request.

server/etcdserver/apply.go

@@ -148,15 +148,15 @@ func (a *applierV3backend) Apply(r *pb.InternalRaftRequest, shouldApplyV3 member
 	case r.ClusterVersionSet != nil: // Implemented in 3.5.x
 		op = "ClusterVersionSet"
 		a.s.applyV3Internal.ClusterVersionSet(r.ClusterVersionSet, shouldApplyV3)
-		return nil
+		return ar
 	case r.ClusterMemberAttrSet != nil:
 		op = "ClusterMemberAttrSet" // Implemented in 3.5.x
 		a.s.applyV3Internal.ClusterMemberAttrSet(r.ClusterMemberAttrSet, shouldApplyV3)
-		return nil
+		return ar
 	case r.DowngradeInfoSet != nil:
 		op = "DowngradeInfoSet" // Implemented in 3.5.x
 		a.s.applyV3Internal.DowngradeInfoSet(r.DowngradeInfoSet, shouldApplyV3)
-		return nil
+		return ar
 	}
 
 	if !shouldApplyV3 {

server/etcdserver/version/version.go

@@ -64,7 +64,7 @@ func (m *Manager) DowngradeEnable(ctx context.Context, targetVersion *semver.Ver
 	if err != nil {
 		return err
 	}
-	return m.s.DowngradeEnable(context.Background(), targetVersion)
+	return m.s.DowngradeEnable(ctx, targetVersion)
 }
 
 // DowngradeCancel cancels ongoing downgrade process.

tests/e2e/cluster_downgrade_test.go

@@ -46,17 +46,17 @@ func TestDowngradeUpgrade(t *testing.T) {
 	validateVersion(t, epc, version.Versions{Cluster: currentVersionStr, Server: currentVersionStr})
 
 	downgradeEnable(t, epc, lastVersion)
+	expectLog(t, epc, "The server is ready to downgrade")
 	validateVersion(t, epc, version.Versions{Cluster: lastVersionStr, Server: currentVersionStr})
 
 	stopEtcd(t, epc)
 	epc = startEtcd(t, lastReleaseBinary, dataDirPath)
-	validateVersion(t, epc, version.Versions{Cluster: lastVersionStr, Server: lastVersionStr})
 	expectLog(t, epc, "the cluster has been downgraded")
+	validateVersion(t, epc, version.Versions{Cluster: lastVersionStr, Server: lastVersionStr})
 
 	stopEtcd(t, epc)
 	epc = startEtcd(t, currentEtcdBinary, dataDirPath)
-	// TODO: Verify cluster version after upgrade when we fix cluster version set timeout
-	validateVersion(t, epc, version.Versions{Server: currentVersionStr})
+	validateVersion(t, epc, version.Versions{Cluster: currentVersionStr, Server: currentVersionStr})
 }
 
 func startEtcd(t *testing.T, execPath, dataDirPath string) *e2e.EtcdProcessCluster {
@@ -100,11 +100,12 @@ func downgradeEnable(t *testing.T, epc *e2e.EtcdProcessCluster, ver semver.Versi
 	}
 	defer c.Close()
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
-	// TODO: Fix request always timing out even thou it succeeds
-	c.Downgrade(ctx, 1, ver.String())
+	_, err = c.Downgrade(ctx, 1, ver.String())
+	if err != nil {
+		t.Fatal(err)
+	}
 	cancel()
 
-	expectLog(t, epc, "The server is ready to downgrade")
 }
 
 func stopEtcd(t *testing.T, epc *e2e.EtcdProcessCluster) {