Add interface comments

Signed-off-by: khanhtc1202 <[email protected]>

pkg/plugin/logpersister/persister.go

@@ -35,11 +35,15 @@ type apiClient interface {
 	ReportStageLogsFromLastCheckpoint(ctx context.Context, in *service.ReportStageLogsFromLastCheckpointRequest, opts ...grpc.CallOption) (*service.ReportStageLogsFromLastCheckpointResponse, error)
 }
 
+// Persister is responsible for saving the stage logs into server's storage.
+// It sends the logs to the piped plugin-api grpc server through the apiClient.
 type Persister interface {
 	Run(ctx context.Context) error
 	StageLogPersister(deploymentID, stageID string) StageLogPersister
 }
 
+// StageLogPersister is a child persister instance for a specific stage.
+// Use this to persist the stage logs and make it viewable on the UI.
 type StageLogPersister interface {
 	Write(log []byte) (int, error)
 	Info(log string)

pkg/plugin/logpersister/persister_test.go

@@ -18,12 +18,13 @@ import (
 	"context"
 	"testing"
 
-	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/cmd/piped/service"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/atomic"
 	"go.uber.org/zap"
 	"google.golang.org/grpc"
+
+	"github.com/pipe-cd/pipecd/pkg/app/pipedv1/cmd/piped/service"
 )
 
 type fakeAPIClient struct {