diff --git a/br/pkg/mock/mock_cluster.go b/br/pkg/mock/mock_cluster.go
index e00246835c365..d1ece26505d05 100644
--- a/br/pkg/mock/mock_cluster.go
+++ b/br/pkg/mock/mock_cluster.go
@@ -6,6 +6,7 @@ import (
 	"database/sql"
 	"fmt"
 	"io"
+	"net"
 	"net/http"
 	"net/http/pprof"
 	"net/url"
@@ -86,18 +87,40 @@ func NewCluster() (*Cluster, error) {
 
 // Start runs a mock cluster.
 func (mock *Cluster) Start() error {
-	statusURL, err := url.Parse(tempurl.Alloc())
-	if err != nil {
-		return errors.Trace(err)
+	var (
+		err       error
+		statusURL *url.URL
+		addrURL   *url.URL
+	)
+	for i := 0; i < 10; i++ {
+		// retry 10 times to get available port
+		statusURL, err = url.Parse(tempurl.Alloc())
+		if err != nil {
+			return errors.Trace(err)
+		}
+		listen, err := net.Listen("tcp", fmt.Sprintf("127.0.0.1:%s", statusURL.Port()))
+		if err == nil {
+			// release port listening
+			listen.Close()
+			break
+		}
 	}
 	statusPort, err := strconv.ParseInt(statusURL.Port(), 10, 32)
 	if err != nil {
 		return errors.Trace(err)
 	}
 
-	addrURL, err := url.Parse(tempurl.Alloc())
-	if err != nil {
-		return errors.Trace(err)
+	for i := 0; i < 10; i++ {
+		addrURL, err = url.Parse(tempurl.Alloc())
+		if err != nil {
+			return errors.Trace(err)
+		}
+		listen, err := net.Listen("tcp", fmt.Sprintf("127.0.0.1:%s", addrURL.Port()))
+		if err == nil {
+			// release port listening
+			listen.Close()
+			break
+		}
 	}
 	addrPort, err := strconv.ParseInt(addrURL.Port(), 10, 32)
 	if err != nil {
diff --git a/br/pkg/trace/tracing_serial_test.go b/br/pkg/trace/tracing_serial_test.go
index 6ddaf3aac1a84..540c73eb38d64 100644
--- a/br/pkg/trace/tracing_serial_test.go
+++ b/br/pkg/trace/tracing_serial_test.go
@@ -20,7 +20,7 @@ func jobA(ctx context.Context) {
 		ctx = opentracing.ContextWithSpan(ctx, span1)
 	}
 	jobB(ctx)
-	time.Sleep(10 * time.Millisecond)
+	time.Sleep(100 * time.Millisecond)
 }
 
 func jobB(ctx context.Context) {
@@ -28,7 +28,7 @@ func jobB(ctx context.Context) {
 		span1 := span.Tracer().StartSpan("jobB", opentracing.ChildOf(span.Context()))
 		defer span1.Finish()
 	}
-	time.Sleep(10 * time.Millisecond)
+	time.Sleep(100 * time.Millisecond)
 }
 
 func TestSpan(t *testing.T) {
@@ -46,7 +46,7 @@ func TestSpan(t *testing.T) {
 	require.NoError(t, err)
 	s := string(content)
 	// possible result:
-	// "jobA      22:02:02.545296  20.621764ms\n"
-	// "  └─jobB  22:02:02.545297  10.293444ms\n"
-	require.Regexp(t, `^jobA.*2[0-9]\.[0-9]+ms\n  └─jobB.*1[0-9]\.[0-9]+ms\n$`, s)
+	// "jobA      22:02:02.545296  200.621764ms\n"
+	// "  └─jobB  22:02:02.545297  100.293444ms\n"
+	require.Regexp(t, `^jobA.*20[0-9]\.[0-9]+ms\n  └─jobB.*10[0-9]\.[0-9]+ms\n$`, s)
 }