br: fix flaky test (#52573)

close #52547

Author: Leavrth

br/pkg/restore/client_test.go

@@ -408,6 +408,10 @@ func TestGetTSWithRetry(t *testing.T) {
 	})
 
 	t.Run("PD leader failure:", func(t *testing.T) {
+		require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/br/pkg/utils/set-attempt-to-one", "1*return(true)"))
+		defer func() {
+			require.NoError(t, failpoint.Disable("github.com/pingcap/tidb/br/pkg/utils/set-attempt-to-one"))
+		}()
 		retryTimes := -1000
 		pDClient := fakePDClient{notLeader: true, retryTimes: &retryTimes}
 		client := restore.NewRestoreClient(pDClient, nil, nil, defaultKeepaliveCfg)

br/pkg/utils/backoff.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	"github.com/pingcap/errors"
+	"github.com/pingcap/failpoint"
 	"github.com/pingcap/log"
 	berrors "github.com/pingcap/tidb/br/pkg/errors"
 	"go.uber.org/zap"
@@ -264,6 +265,9 @@ func (bo *pdReqBackoffer) NextBackoff(err error) time.Duration {
 		}
 	}
 
+	failpoint.Inject("set-attempt-to-one", func(_ failpoint.Value) {
+		bo.attempt = 1
+	})
 	if bo.delayTime > bo.maxDelayTime {
 		return bo.maxDelayTime
 	}