Add election test for background routine handling

server/backend/database/mongo/client.go

@@ -1467,7 +1467,7 @@ func (c *Client) RenewLeaderLease(
 // FindLeader returns the leader hostname for the given leaseLockName.
 func (c *Client) FindLeader(ctx context.Context, leaseLockName string) (*string, error) {
 	electionInfo := &struct {
-		ElectionId    string      `bson:"election_id"`
+		ElectionID    string      `bson:"election_id"`
 		LeaderID      string      `bson:"leader_id"`
 		LeaseExpireAt gotime.Time `bson:"lease_expire_at"`
 	}{}

server/backend/database/mongo/client_test.go

@@ -17,7 +17,9 @@
 package mongo_test
 
 import (
+	"context"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 

server/backend/election/mongo/election.go

@@ -19,6 +19,7 @@ package mongo
 
 import (
 	"context"
+	"sync"
 	"time"
 
 	"github.com/yorkie-team/yorkie/server/backend/database"
@@ -33,6 +34,8 @@ type Elector struct {
 
 	ctx        context.Context
 	cancelFunc context.CancelFunc
+
+	wg sync.WaitGroup
 }
 
 // NewElector creates a new elector instance.
@@ -70,6 +73,7 @@ func (e *Elector) StartElection(
 // Stop stops all leader elections.
 func (e *Elector) Stop() error {
 	e.cancelFunc()
+	e.wg.Wait()
 
 	return nil
 }
@@ -91,7 +95,11 @@ func (e *Elector) run(
 		}
 
 		if acquired {
-			go onStartLeading(ctx)
+			go func() {
+				e.wg.Add(1)
+				onStartLeading(ctx)
+				e.wg.Done()
+			}()
 			logging.From(ctx).Infof(
 				"leader elected: %s", e.hostname,
 			)

server/backend/election/mongo/election_test.go

@@ -2,12 +2,14 @@ package mongo_test
 
 import (
 	"context"
+	"testing"
+	"time"
+
 	"github.com/stretchr/testify/assert"
+
 	"github.com/yorkie-team/yorkie/server/backend/database/mongo"
 	mongoelection "github.com/yorkie-team/yorkie/server/backend/election/mongo"
 	"github.com/yorkie-team/yorkie/test/helper"
-	"testing"
-	"time"
 )
 
 var (
@@ -43,6 +45,7 @@ func TestElection(t *testing.T) {
 		assert.NoError(t, electorA.StartElection(leaseLockName, helper.LeaseDuration, normalTask, stopTask))
 		assert.NoError(t, electorB.StartElection(leaseLockName, helper.LeaseDuration, normalTask, stopTask))
 		assert.NoError(t, electorC.StartElection(leaseLockName, helper.LeaseDuration, normalTask, stopTask))
+		time.Sleep(helper.LeaseDuration)
 
 		// elector A will be the leader because it is the first to start the election.
 		leader, err := db.FindLeader(context.Background(), leaseLockName)
@@ -82,7 +85,7 @@ func TestElection(t *testing.T) {
 		assert.NoError(t, electorB.StartElection(leaseLockName, helper.LeaseDuration, normalTask, stopTask))
 		assert.NoError(t, electorC.StartElection(leaseLockName, helper.LeaseDuration, normalTask, stopTask))
 
-		// check if elector A is still the leader
+		// wait for lease expiration and check if elector A is still the leader while handling a long task
 		time.Sleep(helper.LeaseDuration)
 
 		leader, err := db.FindLeader(context.Background(), leaseLockName)
@@ -92,7 +95,26 @@ func TestElection(t *testing.T) {
 	})
 
 	t.Run("handle background routines when shutting down the server test", func(t *testing.T) {
-		// TODO(krapie): find the way to gradually close election routines
-		t.Skip()
+		shutdownCh := make(chan struct{})
+
+		isTaskDone := false
+		longTask := func(ctx context.Context) {
+			close(shutdownCh)
+			time.Sleep(helper.LeaseDuration)
+			isTaskDone = true
+		}
+
+		elector := mongoelection.NewElector("A", db)
+		assert.NoError(t, elector.StartElection(t.Name(), helper.LeaseDuration, longTask, stopTask))
+
+		// if receive shutdown signal, stop elector
+		select {
+		case <-shutdownCh:
+			assert.NoError(t, elector.Stop())
+		}
+
+		// check if the task is done
+		// this means that the background routine is handled properly after server(elector) is stopped
+		assert.Equal(t, true, isTaskDone)
 	})
 }